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QUIZ
Identités remarquables (méthode)
Exercice n°1
On veut développer l'expression : $(6+y)^2$
Question 1 :
On reconnaît l'identité remarquable :
$(\color{}{a}+\color{}{b})^2 = a^2 + 2\color{}a\color{}b + b^2$ $(\color{}{a}+\color{}{b})(\color{}{a}-\color{}{b}) = a^2 - b^2$ $(\color{}{a}-\color{}{b})^2 = a^2 - 2\color{}a\color{}b + b^2$
Question 2 :
Ici $\color{red}a =$ ?
$-6$ $-36$ $6$ $36$
Question 3 :
Et $\color{green}b = $ ?
$\,y^2$ $-y$ $y$ $-\,y^2$
Question 4 :
$(\color{red}{6}+\color{green}{y})^2 \,$ $=\,\color{red}{6}^2 \,+ 2\times\color{red}{6}\times\color{green}{y} \,+ \color{green}{y}^2$ $= $ ?
$6\, +12\,y\,+ \,y^2$ $36\, +12\,y\,+ y$ $36\, +12\,y\,+ \,y^2$ $36\, +6\,y\,+ \,y^2$
Exercice n°2
On veut développer l'expression : $(-7-x)^2$
$(\color{}{a}-\color{}{b})^2 = a^2 - 2\color{}a\color{}b + b^2$ $(\color{}{a}+\color{}{b})^2 = a^2 + 2\color{}a\color{}b + b^2$ $(\color{}{a}+\color{}{b})(\color{}{a}-\color{}{b}) = a^2 - b^2$
$7$ $49$ $-7$ $-49$
$-\,x^2$ $x$ $\,x^2$ $-x$
$(\color{red}{-7}-\color{green}{x})^2 \,$ $=\,(\color{red}{-7})^2 \,- 2\times\color{red}{(-7\,)}\times\color{green}{x} \,+ \color{green}{x}^2$ $= $ ?
$49\, +14\,x\,+ \,x^2$ $49\, +14\,x\,- \,x^2$ $49\, +14\,x\,+ x$ $49\, -14\,x\,+ \,x^2$
Exercice n°3
On veut développer l'expression : $(-3x+y)(-3x-y)$
$(\color{}{a}+\color{}{b})^2 = a^2 + 2\color{}a\color{}b + b^2$ $(\color{}{a}-\color{}{b})^2 = a^2 - 2\color{}a\color{}b + b^2$ $(\color{}{a}+\color{}{b})(\color{}{a}-\color{}{b}) = a^2 - b^2$
$3x$ $9\,x^2$ $-3\,x^2$ $-3x$
$\,y^2$ $-\,y^2$ $y$
$(\color{red}{-3x}+\color{green}{y})(\color{red}{-3x}-\color{green}{y}) \,$ $=\,(\color{red}{-3x})^2 - \color{green}{y}^2$ $= $ ?
$9\,x^2 \,- 2\,y^2$ $-3\,x^2 \,- \,y^2$ $-9\,x^2 \,- \,y^2$ $9\,x^2 \,- \,y^2$