Ex 8.1, 1
In Δ ABC, right-angled at B, AB = 24 cm, BC = 7 cm. Determine :
sin A, cos A
Step1 : Finding sides of triangle
In right triangle ABC,
Using Pythagoras theorem
(Hypotenuse)2 = (Height)2 + (Base)2
AC2 = AB2 + BC2
AC2 = 242 + 72
AC2 = 576 + 49
AC2 = 625
AC = √𝟔𝟐𝟓
AC = √(25^2 )
AC = 25
Hence AC = 25 cm
Step 2: Finding sin A , cos A
sin A = (𝑠𝑖𝑑𝑒 𝑜𝑝𝑝𝑜𝑠𝑖𝑡𝑒 𝑡𝑜 ∠ 𝐴)/𝐻𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒
= 𝐵𝐶/𝐴𝐶
= 𝟕/𝟐𝟓
cos A = (𝑠𝑖𝑑𝑒 𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 𝑡𝑜 ∠ 𝐴)/𝐻𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒
= 𝐴𝐵/𝐴𝐶
= 𝟐𝟒/𝟐𝟓
Ex 8.1, 1
In Δ ABC, right-angled at B, AB = 24 cm, BC = 7 cm. Determine :
(ii) sin C, cos C
Now,
AC = 25 cm, AB = 24 cm, BC = 7 cm
sin C = (𝑠𝑖𝑑𝑒 𝑜𝑝𝑝𝑜𝑠𝑖𝑡𝑒 𝑡𝑜 ∠ 𝐶)/𝐻𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒
= 𝐴𝐵/𝐴𝐶
= 𝟐𝟒/𝟐𝟓
cos C = (𝑠𝑖𝑑𝑒 𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 𝑡𝑜 ∠ 𝐶)/𝐻𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒
= 𝐵𝐶/𝐴𝐶
= 𝟕/𝟐𝟓

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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