First you subtract from the square of B,
... the product of four times A times C.
The next thing which, you must compute,
... is from that, the exact square root.

Add or subtract it to minus B,
... we're almost done as you shall see.
Divide it all by two times A,
... and the answers are yours, hip hip hooray!

5x²-75x+180 = 0

B² = -75 * -75 = 5625

Minus 4 * A * C = -3600 → 2025

Square root of 2025 = 45

75 + 45 = 120; 75 - 45 = 30

Divide those by 2 * 5 ... and answers are 12 and 3!

5 * 12² - 75 * 12 + 180 = 720 - 900 + 180 = 0.
5 * 3² - 75 * 3 + 180 = 45 - 225 + 180 = 0.