Hello, Dragon!
A different spin on Ron's solution . . .
Find the values of x + y .if x² + y² = 36 and xy = 10
Consider: .(x + y)² .= .x² + 2xy + y² .= .(x² + y²) + 2(xy) .= .36 + 2(10)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .__ . . . . . .__
So we have: .(x + y)² .= .56 . → . x + y .= . ±√56 .= .±2√14