Answer:
Make use of the fact that
.
Explanation:
Start from the given:
.
In other words:
.
Square both sides of the equation:
.
Equality would still hold because:
.
Simplify:
.
.
Subtract
from both sides of this equation:
.
Subtract
from both sides of this equation:
.
Again, square both sides of this equation:
.
.
(by the symmetric property of equalities.)