1) The perimeter is equal to the sum of the lengths of all sides of the triangle, respectively, to find the base of an isosceles triangle, you need to subtract the lengths of the other two sides from its perimeter.
2) In an isosceles triangle, the two sides are equal to 25 cm, so you can find the base: 90 cm – 25 cm – 25 cm = 40 cm.
ANSWER: 40 cm.
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