Answer:
Step-by-step explanation:
You want the side lengths in the right triangle with short side x, long side x+7 and hypotenuse 17.
Pythagorean theorem
Your familiarity with the Pythagorean triple {8, 15, 17} suggests the side lengths are ...
x = 8, AB = 8 cm
BC = 15 cm
Quadratic
In case you're not familiar with that triple, you can find the side lengths using the Pythagorean relation:
17² = x² +(x +7)²
2x² +14x = 240 . . . . . . . . rearrange
x² +7x = 120 . . . . . . . . . . . . . . divide by 2
x² +7x +3.5² = 120 +3.5² . . . . . . complete the square
(x +3.5)² = 132.25 = 11.5²
x +3.5 = 11.5 . . . . . . . . . . . . . . take the positive square root
x = 8 . . . . . . . . . . . . . . . . subtract 3.5
x +7 = 15
The side lengths are AB = 8 cm and BC = 15 cm.