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From the figure (i) given below, calculate all the six t-ratios for both acute angles.

From the figure, calculate all the six t-ratios for both acute angles. Trigonometrical Ratios, ML Aggarwal Understanding Mathematics Solutions ICSE Class 9.

Trigonometrical Ratios

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Answer

In right angle triangle ABC,

By pythagoras theorem we get :

⇒ AC2 = AB2 + BC2

⇒ 32 = AB2 + 22

⇒ 9 = AB2 + 4

⇒ AB2 = 9 - 4

⇒ AB2 = 5

⇒ AB = 5\sqrt{5}.

For angle A,

sin A=PerpendicularHypotenuse=BCAC=23.cos A=BaseHypotenuse=ABAC=53.tan A=PerpendicularBase=BCAB=25.cot A=BasePerpendicular=ABBC=52.sec A=HypotenuseBase=ACAB=35.cosec A=HypotenusePerpendicular=ACBC=32.\Rightarrow \text{sin A} = \dfrac{\text{Perpendicular}}{\text{Hypotenuse}} \\[1em] = \dfrac{BC}{AC} = \dfrac{2}{3}. \\[1em] \Rightarrow \text{cos A} = \dfrac{\text{Base}}{\text{Hypotenuse}} \\[1em] = \dfrac{AB}{AC} = \dfrac{\sqrt{5}}{3}. \\[1em] \Rightarrow \text{tan A} = \dfrac{\text{Perpendicular}}{\text{Base}} \\[1em] = \dfrac{BC}{AB} = \dfrac{2}{\sqrt{5}}. \\[1em] \Rightarrow \text{cot A} = \dfrac{\text{Base}}{\text{Perpendicular}} \\[1em] = \dfrac{AB}{BC} = \dfrac{\sqrt{5}}{2}. \\[1em] \Rightarrow \text{sec A} = \dfrac{\text{Hypotenuse}}{\text{Base}} \\[1em] = \dfrac{AC}{AB} = \dfrac{3}{\sqrt{5}}. \\[1em] \Rightarrow \text{cosec A} = \dfrac{\text{Hypotenuse}}{\text{Perpendicular}} \\[1em] = \dfrac{AC}{BC} = \dfrac{3}{2}. \\[1em]

For angle C,

sin C=PerpendicularHypotenuse=ABAC=53.cos C=BaseHypotenuse=BCAC=23.tan C=PerpendicularBase=ABBC=52.cot C=BasePerpendicular=BCAB=25.sec C=HypotenuseBase=ACBC=32.cosec C=HypotenusePerpendicular=ACAB=35.\Rightarrow \text{sin C} = \dfrac{\text{Perpendicular}}{\text{Hypotenuse}} \\[1em] = \dfrac{AB}{AC} = \dfrac{\sqrt{5}}{3}. \\[1em] \Rightarrow \text{cos C} = \dfrac{\text{Base}}{\text{Hypotenuse}} \\[1em] = \dfrac{BC}{AC} = \dfrac{2}{3}. \\[1em] \Rightarrow \text{tan C} = \dfrac{\text{Perpendicular}}{\text{Base}} \\[1em] = \dfrac{AB}{BC} = \dfrac{\sqrt{5}}{2}. \\[1em] \Rightarrow \text{cot C} = \dfrac{\text{Base}}{\text{Perpendicular}} \\[1em] = \dfrac{BC}{AB} = \dfrac{2}{\sqrt{5}}. \\[1em] \Rightarrow \text{sec C} = \dfrac{\text{Hypotenuse}}{\text{Base}} \\[1em] = \dfrac{AC}{BC} = \dfrac{3}{2}. \\[1em] \Rightarrow \text{cosec C} = \dfrac{\text{Hypotenuse}}{\text{Perpendicular}} \\[1em] = \dfrac{AC}{AB} = \dfrac{3}{\sqrt{5}}. \\[1em]

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