Question

Hi pls help me thankssspls provide me with workings thankss :)​

Answer 1

Step-by-step explanation:

(i)

Using cos(a - b) = cos a cos b + sin a sin b

$\frac{4}{5}$ = cos a cos b + $\frac{1}{5}$

cos a cos b = $\frac{4}{5} -\frac{1}{5} = \frac{3}{5}$

(ii)

Using cos(a + b) = cos a cos b - sin a sin b

cos(a + b) = $\frac{3}{5}-\frac{1}{5}=\frac{2}{5}$

(iii)

Using cot a = $\frac{cos a}{sin a}$

$=(\frac{cos A}{sin A} )(\frac{cos B}{sin B} )$

$=\frac{cos A cos B}{sin A sin B}$

$=\frac{\frac{3}{5} }{\frac{1}{5} }$  $=\frac{3}{5}$ × $5$

= 3

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