Question

if(x+3)(x-b)=x2+7x+a is an identity then find a and b​

Answer 1

Answer:

a=12

b=(-4)

Step-by-step explanation:

(x+3)(x-b)=x2+7x+a [(a+b)(c+d)=(ac)+(ad)+(bc)+(bd)]

(x*x)+(x*-b)+(3*x)+(3*-b)=x2+7x+a

x2-bx+3x-3b=x2+7x+a

(3x-bx)-3b=7x+a [x2 on both sides gets cancelled]

therefore,

3x-bx=7x

(3-b)x=7x

3-b=7. [x on both sides gets cancelled]

b=-4

therefore,

-3b=a

-3(-4)=a

a=12