Evaluate the following: 80^ 20^ + 80^ 20^ - Vidyadip

Question

Evaluate the following: $\cos80^\circ\cos20^\circ+\sin80^\circ\sin20^\circ$

✓

Answer

$=\cos(80^\circ-20^\circ)$$[\cos(\text{A-B})=\cos\text{A}\cos\text{B}+\sin\text{A}\sin\text{B}]$ $=\cos60^\circ$ $=\frac{1}{2}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "(Each question 1 marks)" from Trigonometric Ratios of Multiple and Submultiple Angles→Trigonometric Ratios of Multiple and Submultiple Angles — all question types→MATHS STD 11 Science question papers→Gujarat Board STD 11 Science question papers→Gujarat Board question paper generator→

Similar questions

Write the value of $\lim_\limits{\text{x}\rightarrow\text{c}}\frac{\text{f}(\text{x})-\text{f}(\text{c})}{\text{x}-\text{c}}$

Find the derivative of $x^{-4}\left(3-4 x^{-5}\right)$

Find the derivative at x = 2 of the function f(x) = 3x.

Write the number of parallelograms that can be formed from a set of four parallel lines intersecting another set of three parallel lines.

Find the derivative of function ($x^2 + 1$) cos x (it is to be understood that a, b, c, d, p, q, r and s are fixed non-zero constants and m and n are integers).

$\phi$′ $\cap$ A = ________

Are the following pairs of statements negations of each other: The number x is a rational number. The number x is an irrational number.

Find the derivative of function $(x + cos x) (x - tan x)$ (it is to be understood that $a, b, c, d, p, q, r$ and $s$ are fixed non-zero constants and m and n are integers).

Two dice are thrown. The events A, B and C are as follows:
A: getting an even number on the first die
B: getting on odd number on the first die
C: getting the sum of the numbers on the dice $\leq 5$
Describe the event 'B or C'

Determine the domain and range of the relation R defined by R = {(x, x + 5): x $ \in $ (0, 1, 2, 3, 4, 5)}