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In the adjoining figure, the value of sin B cos C + sin C cos B is

  1. 0

  2. 1

  3. 53\dfrac{5}{3}

  4. 2

In the figure, the value of sin B cos C + sin C cos B is? Trigonometrical Ratios, ML Aggarwal Understanding Mathematics Solutions ICSE Class 9.

Trigonometrical Ratios

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Answer

In right angle triangle ABC,

⇒ BC2 = AB2 + AC2

⇒ 102 = (6)2 + (AC)2

⇒ AC2 = 102 - 62

⇒ AC2 = 100 - 36

⇒ AC2 = 64

⇒ AC = 64\sqrt{64} = 8 cm.

By formula,

sin B = PerpendicularHypotenuse\dfrac{\text{Perpendicular}}{\text{Hypotenuse}}

= ACBC=810\dfrac{AC}{BC} = \dfrac{8}{10}.

sin C = PerpendicularHypotenuse\dfrac{\text{Perpendicular}}{\text{Hypotenuse}}

= ABBC=610\dfrac{AB}{BC} = \dfrac{6}{10}.

cos B = BaseHypotenuse\dfrac{\text{Base}}{\text{Hypotenuse}}

= ABBC=610\dfrac{AB}{BC} = \dfrac{6}{10}.

cos C = BaseHypotenuse\dfrac{\text{Base}}{\text{Hypotenuse}}

= ACBC=810\dfrac{AC}{BC} = \dfrac{8}{10}.

Substituting values in sin B cos C + sin C cos B we get :

sin B cos C + sin C cos B=810×810+610×610=64100+36100=100100=1.\Rightarrow \text{sin B cos C + sin C cos B} = \dfrac{8}{10} \times \dfrac{8}{10} + \dfrac{6}{10} \times \dfrac{6}{10} \\[1em] = \dfrac{64}{100} + \dfrac{36}{100} \\[1em] = \dfrac{100}{100} = 1.

Hence, Option 2 is the correct option.

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