9b. a^4 +2a^2-8=0
factorise
(a^2 + 4)(a^2 - 2)=0
we then get two answers from the brackets
a^2=-4
a= sqrt(-4) or 2j
and the second bracket gives us a^2=2
a= sqrt(2)
11. First expand the brackets.
Ax^3 + Bx^2 - x^2 + Bx +Cx + D
then equate the coefficients, this basically means put all the x^3, x^2 etc values together.
so Ax^3=3x^3 so we know that A=3 Then put the x^2 together, so Bx^2-x^2=-x^2 and rearranging this gives B=0
Next we do Bx+Cx = 2x and we know that B is 0 so we can get rid of it and know that C = 2.
finally we can see that D = -7