Algebra More... XD

Algebra Level 1

Given real numbers A and B such that A^2+B^2 = 2 and AB^2+BA^2 = 2, find A and B.

2 and 0 0 and 0 3 and 3/4 1 and 1

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2 solutions

Christian Daang
Oct 12, 2014

ab(a+b) = 2

ab = 2/(a+b)

let c = a+b

a^2 + b^2 = 2

(a+b)^2 - 2ab = 2

c^2 - 2(2/c) = 2

c^3 - 4 = 2c

c^3 - 2c - 4 = 0

(c-2)(c^2 + 2c + 2) = 0

c = 2

Reject c^2 + 2c + 2 = 0 because it will give a not real solution:

Therefore:

a+b = 2

ab = 1

Going to:

x^2 - 2x + 1 = 0

(x-1)^2 = 0

x = 1

That means:

So, 1 is the 1st root:

a+b = 2 ----> 1+b = 2 -----. b = 1

Therefore:

a = b = 1

Easiest way is to simply plug in the values and eliminate some options by observation .A and B can not be zero because 0 2 + 0 2 2 0^2+0^2\neq2 In the second option,A cannot be 2 because 2 2 + 0 2 2 2^2+0^2\neq2 If we plug in the value of 1 for both A and B in both the equation both equations are satisfied so the answer is 1 a n d 1 \boxed{1\;and\;1}

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