Recordem

1. Errors freqüents

Us indiquem alguns errors que, per l'experiència en les correccions, veiem que feu amb freqüència. Aquests errors són bàsics i greus i es penalitzen. Heu d'intentar no fer-los.

En els apartats següents d'aquest quadern podeu repassar algunes coses bàsiques que heu de recordar, especialment d'equacions.

Errors operacions i signes

$2 times 0 equals bold 2 space space space space space rightwards arrow space space 2 times 0 equals bold 0 2 plus 3 times 6 equals bold 5 bold times bold 6 space space space rightwards arrow space space 2 plus 3 times 6 equals bold 2 bold plus bold 18 bold equals bold 20$

$x minus left parenthesis 3 x plus 5 right parenthesis equals x minus 3 x bold plus 5 space space space rightwards arrow space space x minus left parenthesis 3 x plus 5 right parenthesis equals x minus 3 x bold minus 5$

$1 minus fraction numerator x minus 5 over denominator 2 end fraction equals fraction numerator 2 minus x bold minus 5 over denominator 2 end fraction space space space rightwards arrow space space space 1 minus fraction numerator x minus 5 over denominator 2 end fraction equals fraction numerator 2 minus x bold plus 5 over denominator 2 end fraction$

$left parenthesis x minus 3 right parenthesis squared equals bold italic x to the power of bold 2 bold minus bold 9 bold space bold space bold space bold rightwards arrow bold space space left parenthesis x minus 3 right parenthesis squared equals bold italic x to the power of bold 2 bold minus bold 6 bold italic x bold plus bold 9$

$left parenthesis 5 minus 3 right parenthesis squared equals bold 5 to the power of bold 2 bold minus bold 3 to the power of bold 2 bold space bold space bold space bold rightwards arrow bold space bold space bold space bold left parenthesis bold 5 bold minus bold 3 bold right parenthesis to the power of bold 2 bold equals bold 2 to the power of bold 2 bold equals bold 4 bold space bold space$

Observació: no cal fer $begin mathsize 14px style text (5-3 end text text ) end text squared equals 5 squared minus 2 times 5 times 3 plus 9 equals 25 minus 30 plus 9 equals 4 end style$

$square root of x squared minus 9 end root bold equals bold italic x bold minus bold 3$

$3 over 0 equals bold 0 bold space bold space bold space rightwards arrow space space space space 3 over 0 equals bold infinity$

$2 bold times bold minus bold 3 space space space space rightwards arrow space space space space bold 2 bold times bold left parenthesis bold minus bold 3 bold right parenthesis space space space o space space space bold 2 bold left parenthesis bold minus bold 3 bold right parenthesis$

$negative 2 bold times bold minus bold 3 space space space space rightwards arrow space space space space minus bold 2 bold times bold left parenthesis bold minus bold 3 bold right parenthesis space space space o space space space minus bold 2 bold left parenthesis bold minus bold 3 bold right parenthesis bold space bold space bold space bold space o bold space bold space bold space bold left parenthesis bold minus bold 2 bold right parenthesis bold times bold left parenthesis bold minus bold 3 bold right parenthesis bold space bold space$

$2 times 3 squared equals bold 6 to the power of bold 2 bold equals bold 36 space space space rightwards arrow space space 2 times 3 squared equals bold 2 bold times bold 9 bold equals bold 18$

$negative 2 squared equals bold 4 bold space bold space bold space bold space rightwards arrow space space minus 2 squared equals bold minus bold 4 minus left parenthesis negative 2 right parenthesis squared equals bold 4 bold space bold space bold space bold space bold rightwards arrow bold space minus left parenthesis negative 2 right parenthesis squared equals bold minus bold 4$

$negative 2 squared equals left parenthesis negative 2 right parenthesis squared space space space N O factorial space space space space space rightwards arrow space space space minus 2 squared equals negative 4 comma space space space space space space space left parenthesis negative 2 right parenthesis squared equals 4 space space$

$2 times left parenthesis x minus 3 right parenthesis squared equals bold left parenthesis bold 2 bold italic x bold minus bold 6 bold right parenthesis to the power of bold 2 bold space bold space bold space bold space rightwards arrow space space 2 times left parenthesis x minus 3 right parenthesis squared equals 2 times left parenthesis x squared minus 6 x plus 9 right parenthesis equals 2 x squared minus 12 x plus 18$

$2.3 over 5 equals bold 6 over bold 10 space space space rightwards arrow space space 2.3 over 5 equals 6 over bold 5$

$3 to the power of negative 1 end exponent equals bold minus bold 3 bold space bold space bold space bold space rightwards arrow space space 3 to the power of negative 1 end exponent equals bold 1 over bold 3$

Errors en equacions:

incorrecte correcte

$open square brackets negative 2 x equals 4 space space rightwards double arrow space x equals bold 4 over bold 2 bold equals bold 2 close square brackets space space rightwards arrow space open square brackets negative 2 x equals 4 space space rightwards double arrow space x equals fraction numerator bold 4 over denominator bold minus bold 2 end fraction bold equals bold minus bold 2 close square brackets space space space o space space space open square brackets negative 2 x equals 4 space space rightwards double arrow bold space bold 2 bold italic x bold equals bold minus bold 4 bold space bold space bold rightwards double arrow bold italic x bold equals fraction numerator bold minus bold 4 over denominator bold 2 end fraction bold equals bold minus bold 2 close square brackets space space space space space space space$

$open square brackets table row cell 4 plus x equals 3 x space space rightwards double arrow space x minus 3 x equals bold 4 space end cell blank end table close square brackets space space space space space space rightwards arrow space space space open square brackets x table row cell negative 3 x equals negative 4 space space rightwards double arrow bold minus bold 2 bold italic x bold equals bold minus bold 4 bold space bold space bold space bold rightwards double arrow bold space bold space bold space bold italic x bold equals fraction numerator bold minus bold 4 over denominator bold minus bold 2 end fraction bold equals bold 2 space end cell blank end table close square brackets space space space space space space space$

$open square brackets negative 3 x equals negative 4 space space rightwards double arrow space bold italic x bold equals bold minus bold 4 over bold 3 bold space space close square brackets space space space rightwards arrow space space open square brackets negative 3 x equals negative 4 space space rightwards double arrow bold space bold italic x bold equals fraction numerator bold minus bold 4 over denominator bold minus bold 3 end fraction bold equals bold 4 over bold 3 bold space space close square brackets space space space o space space space space open square brackets negative 3 x equals negative 4 space space rightwards double arrow bold space bold 3 bold italic x bold equals bold 4 bold space bold space bold space bold rightwards double arrow bold italic x bold equals bold 4 over bold 3 bold space space close square brackets space space space$

$open square brackets fraction numerator x minus 1 over denominator x plus 2 end fraction equals 0 space space rightwards double arrow space bold italic x bold plus bold 2 bold equals bold 0 close square brackets space space space rightwards arrow space space open square brackets fraction numerator x minus 1 over denominator x plus 2 end fraction equals 0 space space rightwards double arrow space bold italic x bold minus bold 1 bold equals bold 0 bold space bold space bold rightwards double arrow bold italic x bold equals bold 1 close square brackets space space space$

$open square brackets fraction numerator x minus 1 over denominator x plus 2 end fraction equals 0 space space rightwards double arrow space bold italic x bold minus bold 1 bold equals bold italic x bold plus bold 2 close square brackets space space space rightwards arrow space space open square brackets fraction numerator x minus 1 over denominator x plus 2 end fraction equals 0 space space rightwards double arrow space bold italic x bold minus bold 1 bold equals bold 0 bold space bold space bold rightwards double arrow bold italic x bold equals bold 1 close square brackets space space space$

$open square brackets x squared equals 9 space space rightwards double arrow space bold italic x bold equals bold 3 close square brackets space space space rightwards arrow space space open square brackets x squared equals 9 space space rightwards double arrow space bold italic x bold equals bold plus-or-minus square root of bold 9 bold equals bold plus-or-minus bold 3 close square brackets space$