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Inverse Trigonometric Functions question

2025 · 28 Jan · Shift 1 · Q31
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  5. /2025 · 28 Jan · Shift 1 · Q31

Inverse Trigonometric Functions question

2025 · 28 Jan · Shift 1 · Q31

JEE MainMathematicsInverse Trigonometric FunctionsMCQ+4 / −1
cos⁡(sin⁡−135+sin⁡−1513+sin⁡−13365)\cos \left(\sin ^{-1} \frac{3}{5}+\sin ^{-1} \frac{5}{13}+\sin ^{-1} \frac{33}{65}\right)cos(sin−153​+sin−1135​+sin−16533​) is equal to:
  1. A
    3365\frac{33}{65}6533​
  2. B
    1
  3. C
    3265\frac{32}{65}6532​
  4. D
    0
View written solutionFree

Correct answer: D

  1. Let A=sin⁡−1(35),B=sin⁡−1(513),C=sin⁡−1(3365).A=\sin^{-1}\left(\frac35\right),\quad B=\sin^{-1}\left(\frac5{13}\right),\quad C=\sin^{-1}\left(\frac{33}{65}\right).A=sin−1(53​),B=sin−1(135​),C=sin−1(6533​). We need to find cos⁡(A+B+C).\cos(A+B+C).cos(A+B+C).

  2. Since A,B,C∈[−π2,π2]A,B,C\in\left[-\frac\pi2,\frac\pi2\right]A,B,C∈[−2π​,2π​], their cosines are positive: cos⁡A=1−(35)2=45,\cos A=\sqrt{1-\left(\frac35\right)^2}=\frac45,cosA=1−(53​)2​=54​, cos⁡B=1−(513)2=1213,\cos B=\sqrt{1-\left(\frac5{13}\right)^2}=\frac{12}{13},cosB=1−(135​)2​=1312​, cos⁡C=1−(3365)2=5665.\cos C=\sqrt{1-\left(\frac{33}{65}\right)^2}=\frac{56}{65}.cosC=1−(6533​)2​=6556​.

  3. First compute sin⁡(A+B)\sin(A+B)sin(A+B) and cos⁡(A+B)\cos(A+B)cos(A+B): sin⁡(A+B)=sin⁡Acos⁡B+cos⁡Asin⁡B\sin(A+B)=\sin A\cos B+\cos A\sin Bsin(A+B)=sinAcosB+cosAsinB =35⋅1213+45⋅513=\frac35\cdot\frac{12}{13}+\frac45\cdot\frac5{13}=53​⋅1312​+54​⋅135​ =3665+2065=5665.=\frac{36}{65}+\frac{20}{65}=\frac{56}{65}.=6536​+6520​=6556​.

    cos⁡(A+B)=cos⁡Acos⁡B−sin⁡Asin⁡B\cos(A+B)=\cos A\cos B-\sin A\sin Bcos(A+B)=cosAcosB−sinAsinB =45⋅1213−35⋅513=\frac45\cdot\frac{12}{13}-\frac35\cdot\frac5{13}=54​⋅1312​−53​⋅135​ =4865−1565=3365.=\frac{48}{65}-\frac{15}{65}=\frac{33}{65}.=6548​−6515​=6533​.

  4. Now compute cos⁡(A+B+C)\cos(A+B+C)cos(A+B+C): cos⁡(A+B+C)=cos⁡(A+B)cos⁡C−sin⁡(A+B)sin⁡C.\cos(A+B+C)=\cos(A+B)\cos C-\sin(A+B)\sin C.cos(A+B+C)=cos(A+B)cosC−sin(A+B)sinC.

    Substituting values, cos⁡(A+B+C)=3365⋅5665−5665⋅3365=0.\cos(A+B+C)=\frac{33}{65}\cdot\frac{56}{65}-\frac{56}{65}\cdot\frac{33}{65}=0.cos(A+B+C)=6533​⋅6556​−6556​⋅6533​=0.

  5. Therefore, cos⁡(sin⁡−135+sin⁡−1513+sin⁡−13365)=0.\cos \left(\sin ^{-1} \frac{3}{5}+\sin ^{-1} \frac{5}{13}+\sin ^{-1} \frac{33}{65}\right)=0.cos(sin−153​+sin−1135​+sin−16533​)=0.

  6. Option check:

    • A: 3365\frac{33}{65}6533​ ❌
    • B: 111 ❌
    • C: 3265\frac{32}{65}6532​ ❌
    • D: 000 ✅

Hence, the correct answer is D.

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