8. Introduction to Trigonometry
medium

निम्नलिखित सर्वसमिका सिद्ध कीजिए, जहाँ वे कोण, जिनके लिए व्यंजक परिभाषित है, न्यून कोण है :

$(\sin A+\operatorname{cosec} A)^{2}+(\cos A+\sec A)^{2}=7+\tan ^{2} A+\cot ^{2} A$

Option A
Option B
Option C
Option D

Solution

$(\sin A+\operatorname{cosec} A)^{2}+(\cos A+\sec A)^{2}=7+\tan ^{2} A+\cot ^{2} A$

$L.H.S.=(\sin A+\operatorname{cosec} A)^{2}+(\cos A+\sec A)^{2}$

$\quad=\sin ^{2} A+\operatorname{cosec}^{2} A+2 \sin A \operatorname{cosec} A+\cos ^{2} A+\sec ^{2} A+2 \cos A \sec A$

$\quad=\left(\sin ^{2} A+\cos ^{2} A\right)+\left(\operatorname{cosec}^{2} A+\sec ^{2} A\right)+2 \sin A\left(\frac{1}{\sin A}\right)+2 \cos A\left(\frac{1}{\cos A}\right)$

$\quad=(1)+\left(1+\cot ^{2} A+1+\tan ^{2} A\right)+(2)+(2)$

$\quad=7+\tan ^{2} A+\cot ^{2} A$

$=R \cdot H . S.$

Standard 10
Mathematics

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