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JEE Main 2024
Trigonometric Equations
Trigonometric Equations
Medium

Question

Let for some real numbers α\alpha and β\beta, a=αiβa = \alpha - i\beta . If the system of equations 4ix+(1+i)y=04ix + (1 + i)y = 0 and 8(cos2π3+isin2π3)x+ay=08\left( {\cos {{2\pi } \over 3} + i\sin {{2\pi } \over 3}} \right)x + \overline a y = 0 has more than one solution, then αβ{\alpha \over \beta } is equal to

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Solution

Given a=αiβa = \alpha - i\beta and 4ix+(1+i)y=04ix + (1 + i)y = 0 ...... (i) 8(cos2π3+isin2π3)x+ay=08\left( {\cos {{2\pi } \over 3} + i\sin {{2\pi } \over 3}} \right)x + \overline a y = 0 .... (ii) By (i) xy=(1+i)4i{x \over y} = {{ - (1 + i)} \over {4i}} ...... (iii) By (ii) xy=a8(12+3i2){x \over y} = {{ - \overline a } \over {8\left( {{{ - 1} \over 2} + {{\sqrt 3 i} \over 2}} \right)}} ..... (iv) Now by (iii) and (iv) 1+i4i=a4(1+3i){{1 + i} \over {4i}} = {{\overline a } \over {4\left( { - 1 + \sqrt 3 i} \right)}} a=(31)+(3+1)i \Rightarrow \overline a = \left( {\sqrt 3 - 1} \right) + \left( {\sqrt 3 + 1} \right)i α+iβ=(31)+(3+1)i \Rightarrow \alpha + i\beta = \left( {\sqrt 3 - 1} \right) + \left( {\sqrt 3 + 1} \right)i \therefore αβ=313+1=23{\alpha \over \beta } = {{\sqrt 3 - 1} \over {\sqrt 3 + 1}} = 2 - \sqrt 3

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