(-3i) (-4i) =
-3 * - 4 * i * i =
12 * i^2 ⇒ [ i^2 = -1 ]
12 * -1 =
-12
x + y = 5 ⇒ y = 5 - x (1)
x^2 + y^2 = 25 (2)
Sub (1) into (2)
x^2 + ( 5 - x) ^2 = 25
x^2 + x^2 - 10x + 25 = 25 subtract 25 from both sides
2x^2 - 10x = 0 factor
2x ( x - 5) set both facoters to 0 and solve for x and x = 0 or x = 5
Using (1)
When x = 0, y = 5 - 0 = 5
and
When x = 5, y = 5 - 5 = 0
So the solutions are (0, 5) and (5, 0 )