Question

if (x+2) and (x-2) are factors of ax4 +2x2 -3x2 +bx-4,then what is the value of a+b.

Answer 1

Put the value of x=2 in equ then
4a+4-6+2b-4
4a+2b-6 mark as 1
Now put the value of x=-2 in equ then
4a+4-6-2b-4
4a-2b-6 mark as 2
Now solve these equations
Adding both
8a-12=0
8a=12
a=12/8=3/2
Subtract equ 2 from 1
4b=0
b=0

Answer 2

x-2=0
x=2
Put the value of x=2 in eqn 
$a(2)^4+2(2)^2-6+b(2)-4=0$
16a+8-6+2b-4=0
16a+2b-2=0
16a=-2b+2-------------------------------eqn (1)

x+2=0
x=-2
Now put the value of x=-2 in eqn then
$a(-2)^4+2(-2)^2-6+b(-2)-4=0$
16a+2-4-2b=0
16a=2b+2----------------------------eqn(2)

ON COMPARING BOTH SIDE
16a+16a=2b+2-2b+2
32a=4
a=1/8

b= > 16*1/8=2b+2
b=>  2-2=2b
b= 1/2