Cossin 18^∘/cos 72^∘ =sin (90^∘ 72^∘)/cos 72^∘ (As, sin (90^∘ A) = cos A) =cos 72^∘/cos 72^∘ = 1 ...

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Standard X

Mathematics

Complementary Trigonometric Ratios

sin 118∘/cos ...

Question

$\frac{s i n 18^{\circ}}{c o s 72^{\circ}}$ ___

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Solution

$c o s \frac{s i n 18^{\circ}}{c o s 72^{\circ}}$
$= \frac{s i n (90^{\circ} - 72^{\circ})}{c o s 72^{\circ}}$

$(A s, s i n (90^{\circ} - A) = c o s A)$
$= \frac{c o s 72^{\circ}}{c o s 72^{\circ}} = 1$

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sin18∘cos72∘___

cossin18∘cos72∘ =sin(90∘−72∘)cos72∘ (As, sin(90∘−A)=cosA) =cos72∘cos72∘=1

$\frac{s i n 18^{\circ}}{c o s 72^{\circ}}$ ___

$c o s \frac{s i n 18^{\circ}}{c o s 72^{\circ}}$
$= \frac{s i n (90^{\circ} - 72^{\circ})}{c o s 72^{\circ}}$

$(A s, s i n (90^{\circ} - A) = c o s A)$
$= \frac{c o s 72^{\circ}}{c o s 72^{\circ}} = 1$