Find a right-angled triangle if one leg is 25 mm and the other is twice as large.

Finding a triangle means calculating all of its sides and angles.
The triangle is rectangular and to calculate the hypotenuse, you can use the Pythagorean theorem, if its one leg is 25 mm, and the second is twice as large or 25 * 2 = 50 mm, then the hypotenuse is (25 ^ 2 + 50 ^ 2) ^ 0.5 = 25 (3) ^ (0.5) mm.
The sine of one of the angles is equal to the ratio of the leg 25 mm to the hypotenuse 25 3 ^ (0.5) mm:
sin A = 25/25 3 ^ (0.5) = 3 ^ (0.5) / 3, which is approximately 0.577.
The angle is about 35 degrees and the second angle is 55.