"The perimeter of an isosceles triangle is 40, and the base is 10. find the length of one of the equial sides."
Perimeter=Base+Side+Side Thence; 40=B+S+S We know S and S [two sides] are the same, because the triangle is an isosceles. The equation thence yields: 40=B+2S B is 10: 40=10+2S minus 10 to both sides 30=2S divide both sides by 2 15=S each side is 15. let's check: 2(15)+10=40 30+10=40 40=40 :-D it works.