Question

using identity (x+a)(x+b)= x²+(a+b)x+ab​

Answer 1

Answer:

(x+a)(x+b)= x²+(a+b)x+ab

(x+(-4)(x+9)=x²+(-4)+9)x+(-4)(9)

=x²+13x+(-36)

= x²+13x-36

Step-by-step explanation:

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Answer 2

Answer:

$\left(x+a\right)\left(x+b\right)=x^2+\left(a+b\right)x+ab\quad :\quad \mathrm{True\:for\:all}\:x$

Step-by-step explanation:

$\left(x+a\right)\left(x+b\right)=x^2+\left(a+b\right)x+ab$

$x^2+bx+ax+ab=x^2+ax+bx+ab$

$\mathrm{Subtract\:}ab\mathrm{\:from\:both\:sides}$

$x^2+bx+ax+ab-ab=x^2+ax+bx+ab-ab$

$x^2+bx+ax=x^2+ax+bx$

$\mathrm{Subtract\:}x^2+ax+bx\mathrm{\:from\:both\:sides}$

$x^2+bx+ax-\left(x^2+ax+bx\right)=x^2+ax+bx-\left(x^2+ax+bx\right)$

$0=0$

HOPE IT HELPS

Eva*