Question 975930
If you mean:
a+b+15=36
a^2+b^2=15
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a + b = 21 --> b = 21-a
a^2 + b^2 = 21
Sub for b
{{{a^2 + (21-a)^2 = 21}}}
{{{2a^2 - 42a + 420 = 0}}}
*[invoke solve_quadratic_equation 2,-42,420]
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{{{a = 21/2 +-sqrt(-1596)/4}}}
{{{a = 21/2 +-i*sqrt(399)/2}}}
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b = conjugate of a