I used the U-substitution

Question

t^8 + 3t^4 - 40

t^8 = u^2 t^4 = u

u^2 + 3u - 40

(u - 5)(u + 8)

(t^4 - 5) (t^4 +8)

Is this correct?

Answer 1

yupp that's right :)