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8. Introduction to Trigonometry
easy
$\triangle ABC$ માં $\angle C$ કાટખૂણો હોય, તો $\cos ( A + B )$ નું મૂલ્ય ......... છે.
A
$1$
B
$\frac{1}{2}$
C
$\frac{\sqrt{3}}{2}$
D
$0$
Solution
We know that, in $\triangle A B C$, sum of three angles $=180^{\circ}$
i.e. $\angle A+\angle B+\angle C=180^{\circ}$
But right angled at $C$ i.e., $\angle C=90^{\circ}$ [given]
$\angle A+\angle B+90^{\circ}=180^{\circ}$
$A+B=90^{\circ}$ $[\because \angle A=A]$
$\cos (A+B)=\cos 90^{\circ}=0$
Standard 10
Mathematics
