Ch 8 introduces trigonometric ratios of acute angles in right triangles. Students learn the six ratios (sin, cos, tan, cosec, sec, cot), values at standard angles, complementary angle relationships, and fundamental identities.
In a right triangle with angle θ: sin θ = opposite/hypotenuse, cos θ = adjacent/hypotenuse, tan θ = opposite/adjacent. Also: cosec θ = 1/sin θ, sec θ = 1/cos θ, cot θ = 1/tan θ.
sin 0°=0, sin 30°=1/2, sin 45°=1/√2, sin 60°=√3/2, sin 90°=1. cos values are reversed: cos 0°=1, cos 30°=√3/2, cos 45°=1/√2, cos 60°=1/2, cos 90°=0.
sin²θ + cos²θ = 1. 1 + tan²θ = sec²θ. 1 + cot²θ = cosec²θ. Complementary: sin(90°−θ) = cos θ, tan(90°−θ) = cot θ, sec(90°−θ) = cosec θ.
Download: https://ncert.nic.in/textbook/pdf/jemh108.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jemh1ps.zip
By Pythagoras theorem: opposite² + adjacent² = hypotenuse². Dividing both sides by hypotenuse²: (opp/hyp)² + (adj/hyp)² = 1, which is sin²θ + cos²θ = 1.
Book a Trial + Diagnostic session. Get a personalized Learning Path with clear milestones, tutor match, and a plan recommendation — all within 24 hours.
Book Trial + Diagnostic →