Trigonometric Ratios(Qns.& Ans) V.S.A.Q.’S
Trigonometric Ratios(Qns.& Ans) V.S.A.Q.’S designed by the ‘Basics in Maths‘ team.These notes to do help intermediate First-year Maths students. Inter Maths – 1A two marks questions and solutions are very useful in I.P.E examinations. Trigonometric Ratios Up to Transformations Question 1 Find the value of sin2(π/10) + sin2(4π/10) + sin2(6π/10) + sin2(9π/10) Sol: sin2(π/10) + sin2(4π/10) + sin2(6π/10) + sin2(9π/10) = sin2(π/10) + sin2(π/2 – π/10) + sin2(π/2+ π/10) + sin2(π – π/10) = sin2(π/10) + cos2(π/10) + cos2(π/10) + sin2(π/10) = 1 + 1 = 2 Question 2 If sin θ = 4/5 and θ not in the first quadrant, find the value of cos θ Sol: Given sin θ = 4/5 and θ not in the first quadrant ⇒ θ in the second quadrant ⇒ cos θ < 0 cos2θ = 1 – sin2 θ =1 – (4/5)2 = 1 – 16/25 ∴cos θ = – 3/5 (∵cos θ < 0) Question 3 If 3sin θ + 4 cos θ = 5, then find the value of 4 sin θ – 3cos θ Sol: Given, 3sin θ + 4 cos θ = 5 let 4 sin θ – 3cos θ = x (3sin θ + 4 cos θ )2 + (4 sin θ – 3cos θ)2 = 52 + x2 9 sin2 θ + 16 cos2 θ + 12 sin θ cos θ + 16 sin2 θ + 9 cos2 θ – 12sin θ cis θ = 25 + x2 25 sin2 θ + 25 cos2 θ = 25 + x2 25 = 25 + x2 ⇒ x2 = 0 x = 0 ∴ 4 sin θ – 3cos θ = 0 Question 4 If sec θ + tan θ =, find the value of sin θ and determine the quadrant in which θ lies Sol: Given, sec θ + tan θ = ———— (1) We know that sec2 θ – tan2 θ = 1 ⇒ (sec θ + tan θ) (sec θ – tan θ) = 1 sec θ – tan θ = ⇒ sec θ – tan θ = ———— (2) (1) + (2) ⇒ (sec θ + tan θ) + (sec θ – tan θ) = 2sec θ = sec θ = (1) – (2) ⇒ (sec θ + tan θ) – (sec θ – tan θ) = 2 tan θ = ⇒ tan θ = Now sin θ = tan θ ÷ sec θ = Sin θ = Since sec θ positive and tan θ is negative θ lies in the 4th quadrant. Question 5 Prove that cot (π/16). cot (2π/16). cot (3π/16).… cot (7π/16) = 1 Sol: cot (π/16). cot (2π/16). cot (3π/16).… cot (7π/16) = cot (π/16). cot (2π/16). cot (3π/16). cot (4π/16). cot (5π/16) cot (6π/16) cot (7π/16) = cot (π/16). cot (2π/16). cot (3π/16). cot (π/4). cot (π/2 – 3π/16) cot (π/2 – 2π/16) cot (π/2 – π/16) = cot (π/16). cot (2π/16). cot (3π/16). cot (π/4). tan (3π/16) tan (2π/16) tan (π/16) = [cot (π/16). tan (π/16)] [cot (2π/16). tan (2π/16)] [cot (3π/16). tan (3π/16]. cot (π/4) = 1.1.1.1 =1 Question 6 If cos θ + sin θ = cos θ, then prove that cos θ – sin θ = sin θ Sol: Given, cos θ + sin θ = cos θ Sin θ = cos θ – cos θ = ( – 1) cos θ ( + 1) sin θ = ( + 1) ( – 1) cos θ sin θ + sin θ = cos θ ∴ cos θ – sin θ = sin θ Question 7 Find the value of 2(sin6 θ + cos6 θ) – 3 (sin4 θ + cos4 θ) Sol: 2(sin6 θ + cos6 θ) – 3 (sin4 θ + cos4 θ) = 2[(sin2 θ)3 + (cos2 θ)3] – 3[(sin2 θ)2 + (cos2)2 = 2[(sin2 θ + cos2 θ)3 – 3 sin2 θ cos2 θ (sin2 θ + cos2 θ)] – 3[(sin2 θ + cos2 θ)2 – 2 sin2 θ cos2 θ] = 2[1 – 3 sin2 θ cos2 θ] – 3 [1 – 2 sin2 θ cos2 θ] = 2 – 6 sin2 θ cos2 θ – 3 + 6 sin2 θ cos2 θ = – 1 Question 8 If tan 200 = λ, then show that Sol: Given tan 200 = λ = = = = Question 9 If sin α + cosec α = 2, find the value of sinn α + cosecn α, n∈ Z Sol: Given sin α + cosec α = 2 ⇒ sin α + 1/ sin α = 2 ⇒ = 2 sin2 α + 1= 2 sin α sin2 α – 2 sin α + 1= 0 (sin α – 1 )2 = 0 ⇒ sin α – 1 = 0 sin α = 1 ⇒ cosec α = 1 sinn α + cosecn α = (1)n + (1)n =1 + 1 =2 ∴ sinn α + cosecn α = 2 Question 10 Evaluate sin2 + cos2 – tan2 Sol: Question 11 Find the value of sin 3300. cos 1200 + cos 2100. Sin 3000 Sol: sin 3300. cos 1200 + cos 2100. Sin 3000 =sin (3600 – 300). cos (1800 – 600) + cos (1800 + 300). sin (3600 – 600) = (– sin 300). (– cos 600) + (– cos300). (– sin600) = sin 300. cos 600 + cos300. Sin600 = sin (600 + 300) = sin 900 =1 Question 12 Prove that cos4 α + 2 cos2 α = (1 – sin4 α) Sol: cos4 α + 2 cos2 α = cos4 α + 2 cos2 α (1 – cos2 α) = (cos2 α)2 + 2 (1 – sin2 α) (sin2 α) = (1 – sin2 α)2 + 2 sin2 α – 2sin4 α = 1 + sin4 α – 2 sin2 α + 2 sin2 α – 2sin4 α = 1 – sin4 α Question 13 Eliminate θ from x =










