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QJEEM07Ma2cf8: JEE Main 2007 Mathematics - Class 12 JEEM07Ma2cf8 Solution: If and are positive real numbers such that , then the maximum…

If pp and qq are positive real numbers such that p2+q2=1{p^2} + {q^2} = 1 , then the maximum value of (p+q)(p+q) is

Multiple Choice Options

  • A 12{1 \over 2}
  • B 12{1 \over {\sqrt 2 }}
  • C 2{\sqrt 2 }
  • D 22

Step-by-Step Verified Solution

Given that p2+q2=1{p^2} + {q^2} = 1

∴\therefore p=cos⁡θp = \cos \theta and q=sin⁡θq = \sin \theta

Then p+qp+q =cos⁡θ+sin⁡θ= \cos \theta + \sin \theta

We know that

−a2+b2≤acos⁡θ+bsin⁡θ≤a2+b2- \sqrt {{a^2} + {b^2}} \le a\cos \theta + b\sin \theta \le \sqrt {{a^2} + {b^2}}

∴\therefore −2≤cos⁡θ+sin⁡θ≤2- \sqrt 2 \le \cos \theta + \sin \theta \le \sqrt 2

Hence max. value of p+qp + q is 2\sqrt 2

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