Question

If a+b=7 and ab=12 then a^4-b^4=?

Answer 1

Answer:

175 or -175

Find the attachement below, I showed my working out

Answer 2

Answer:

+175 or -175

Step-by-step explanation:

a + b = 7

b = (7 - a)  

ab = 12

a*(7 - a) = 12  [Substituting b = (7-a) ]

7a - a^2 = 12

a^2 - 7a + 12 = 0

a^2 - 4a - 3a + 12 = 0

a(a - 4) - 3(a - 4) = 0

(a - 4)(a - 3) = 0

Therefore, we get a = 4 and a = 3 as solutions

If a = 4,  b = (7 - a) = 3

a^4 - b^4 = 4^4 - 3^4 = 256 - 81 = 175

If a = 3, b = 4

a^4 - b^4 = 3^4 - 4^4 = 81 - 276 = -175