Question 183652
A 25-foot ladder is placed against a building. The bottom of the ladder is 7 feet from the building. If the top of the ladder slips down 4 feet, how many feet will the bottom slide out? (It is not 4 feet). 
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What you had is before the slip:
Let x = height where the ladder hits the building
7 squared+x squared=25 squared
49+x squared=625
x squared=576
x=24 feet 
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NOW, if it slips 4 feet -- that 24-4=20 feet
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Let x = distance from wall:
x^2 + 20^2 = 25^2
x^2 + 400 = 625
x^2 = 225
x = 15 feet 
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But wait, the problem asked: "how many feet will the bottom slide out?"
Since, originally it was 7 feet from the wall
and now it is 15 feet
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The answer is 8 feet.