Algebra

Algebra Level 2

If x + y > 5 x+y>5 and x y > 3 x-y>3 , then which of the options is the range of x x ?

x > 5 x>5 x > 3 x>3 x < 3 x<3 x > 4 x>4

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2 solutions

Aaryan Maheshwari
Jul 21, 2017

x + y > 5 x+y>5 and x y > 3 x-y>3 .

Multiplying both the equations, we get:

x 2 y 2 = 5 × 3 = 15 \implies\space x^2-y^2=5\times3=15 . Now, we know that y 2 y^2 must be at least 1 1 . To find minimum value of x x , let us take y 2 = 1 y^2=1 . So, we have:

x 2 = 15 + y 2 = 15 + 1 = 16 x > 4 \therefore\space x^2=15+y^2=15+1=16\space \implies\space x>4 .

Edward Adan
Mar 3, 2017

x+y>5 x-y>3 then adding, 2x>8 therefore, x>4

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