question about pythagorean theorem

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12181900: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Wed Nov 30, 2011 2:30 am

by 12181900 » Fri Feb 03, 2012 7:33 pm

this is a dumb question but i need to know so that i don't make mistakes in the future.

the first time i saw pythagorean theorem i wanted to square root both sides so that i ended up with a + b = c , like i would with any other algebraic equation.

can anyone please tell me why this is wrong? and should i not do this in the future with similar algerbraic equations?

thanks for your help.

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Source: Beat The GMAT — Problem Solving | Fri Feb 03, 2012 7:33 pm

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Fri Feb 03, 2012 7:40 pm

12181900 wrote:this is a dumb question but i need to know so that i don't make mistakes in the future.

the first time i saw pythagorean theorem i wanted to square root both sides so that i ended up with a + b = c , like i would with any other algebraic equation.

can anyone please tell me why this is wrong? and should i not do this in the future with similar algerbraic equations?

thanks for your help.

Pythagorean Theorem states that hypotenuseÂ² = sum of the squares of the other two sides
If c = hypotenuse, and a and b are the other two sides, then cÂ² = aÂ² + bÂ²
If you take square root on both sides, then c = âˆš(aÂ² + bÂ²) and not c = a + b.

We can take an example, 5 = hypotenuse and 3 and 4 are the other two sides
Then 5Â² = 3Â² + 4Â²
Taking square root on left hand side = 5
Square root on right hand side = âˆš(3Â² + 4Â²) = âˆš(9 + 16) = âˆš25 = 5

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12181900: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Wed Nov 30, 2011 2:30 am

by 12181900 » Fri Feb 03, 2012 7:47 pm

Thanks!

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Fri Feb 03, 2012 7:47 pm

12181900 wrote:Thanks!

You are welcome.

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ronnie1985: Legendary Member; Posts: 626; Joined: Fri Dec 23, 2011 2:50 amFollowed by: 10 members; Location: Ahmedabad; Thanked: 31 times

by ronnie1985 » Sat Feb 04, 2012 2:41 am

(a+b)^2 = (a+b)*(a+b) = a*a + a*b + b*a + b*b = a^2 + a*b + a*b +b^2 = a^2 +2a*b + b^2

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