Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Trigonometry

Question:

If \(\frac{sinx}{siny}\)=\(\frac{1}{2}\) and \(\frac{cosx}{cosy}\)=\(\frac{3}{2}\), then

find the value of cot2x + sin2x.

Options:

\(\frac{889}{162}\)

\(\frac{889}{160}\)

\(\frac{821}{225}\)

1

Correct Answer:

\(\frac{889}{160}\)

Explanation:

⇒ \(\frac{sinx}{siny}\)=\(\frac{1}{2}\) ⇒ 2sinx = siny  ....(1)

⇒ \(\frac{cosx}{cosy}\)=\(\frac{3}{2}\) ⇒ 2cosx = 3cosy  ...(2)

Squaring and Adding eq. (1) & (2)

4sin2x = sin2y

4cos2x = 9cos2y

⇒ 4sin2x + 4cos2x = sin2y + 9cos2y

4(sin2x + cos2x) = sin2y + 9cos2y

4 = sin2y + cos2y + 8cos2y                            [sin2θ + cos2θ = 1]

4 = 1 + 8cos2y

3 = 8cos2y

\(\frac{3}{8}\) = cos2y

cosy = \(\frac{\sqrt {3}}{\sqrt {8}}\)

Now, if we divide both given equation we get:

tanx . coty= \(\frac{1}{3}\)

tanx × \(\frac{\sqrt {3}}{\sqrt {5}}\) = \(\frac{1}{3}\)

tanx = \(\frac{\sqrt {5}}{3\sqrt {3}}\) = \(\frac{P}{B}\)

H = \(\sqrt {(3\sqrt {3})^2 + (\sqrt {5})^2}\)

H = 4\(\sqrt {2}\)

Put in & find out:

⇒ cot2x + sin2x = (\(\frac{3\sqrt {3}}{\sqrt {5}}\))2 + (\(\frac{\sqrt {5}}{4\sqrt {2}}\))2 \(\frac{889}{160}\)