Answer:
see below (I hope this helps!)
Step-by-step explanation:
p² = 4x² * (q(1 + r² / y²) / S)
p²S = 4x² * q(1 + r² / y²)
p²S / 4x²q = 1 + (r² / y²)
p²S / 4x²q - 1 = r² / y²
y² = r² / (p²S / 4x²q - 1)
y = √( r² / (p²S / 4x²q - 1) = √(r²4x²q / (p²S - 4x²q))
