Express the magnitude squared of the cross product of vectors a & b in terms of |a|, |b| and cos(Theta)

Question

Question is most clear in the image. Please help, thank you very much

enter image description here

Answer 1

$|a\times b| = |a||b|\sin\theta$, so $|a\times b|^2 = |a|^2 |b|^2 \sin^2\theta = |a|^2 |b|^2 (1-\cos^2\theta)$.

Answer 2

$|a|^2|b|^2(1-\cos^2\theta)$, since $|a×b|=|a||b|\sin\theta$.