Question

$\left|\begin{array}{cc}cos15^{\circ }& sin15^{\circ }\\ sin75^{\circ }& cos75^{\circ }\end{array}\right|=$

• A. 0
• B. 5
• C. 3
• D. 7

Answer 1

Answer: (A)

We have
$\left|\begin{array}{cc}cos15^{\circ }& sin15^{\circ }\\ sin75^{\circ }& cos75^{\circ }\end{array}\right|=$
$=cos75^{\circ }cos15^{\circ }-sin75^{\circ }sin15^{\circ }=cos\left(75^{\circ }+15^{\circ }\right)$
$=cos90^{\circ }=0$