Question:
(3cos260° + 2cot230° – 5sin245°) = ?
(a) 1
(b) 4
(c) $\frac{17}{4}$
(d) $\frac{13}{6}$
Solution:
As we know that,
$\sin 45^{\circ}=\frac{1}{\sqrt{2}}$
$\cos 60^{\circ}=\frac{1}{2}$
$\cot 30^{\circ}=\sqrt{3}$
By substituting these values, we get
$\left(3 \cos ^{2} 60^{\circ}+2 \cot ^{2} 30^{\circ}-5 \sin ^{2} 45^{\circ}\right)=3\left(\frac{1}{2}\right)^{2}+2(\sqrt{3})^{2}-5\left(\frac{1}{\sqrt{2}}\right)^{2}$
$=3\left(\frac{1}{4}\right)+2(3)-5\left(\frac{1}{2}\right)$
$=\frac{3}{4}+6-\frac{5}{2}$
$=\frac{3+24-10}{4}$
$=\frac{17}{4}$
Hence, the correct option is (c).