Simple Algebra problems

Algebra Level 3

solve:


The answer is 2015.

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3 solutions

W e k n o w t h a t 1 a + 1 b = 6 M u l t i p l y i n g b o t h s i d e s w i t h a b , w e g e t a + b = 6 a b B u t , a + b = 6 S o , 6 = 6 a b o r , a b = 1 N o w , s q u a r i n g b o t h s i d e s o f a + b = 6 a 2 + b 2 + 2 a b = 36 a 2 + b 2 + 2 = 36 a 2 + b 2 = 34 N o w s o l v i n g t h e g i v e n e q u a t i o n , a b + b a + 1981 a 2 + b 2 a b + 1981 34 1 + 1981 2015 We\quad know\quad that\quad \frac { 1 }{ a } +\frac { 1 }{ b } =6\\ Multiplying\quad both\quad sides\quad with\quad ab,\quad we\quad get\\ a+b=6ab\\ But,\quad a+b=6\\ So,\quad 6=6ab\\ or,\quad ab=1\\ \\ Now,\quad squaring\quad both\quad sides\quad of\quad a+b=6\\ { a }^{ 2 }+{ b }^{ 2 }+2ab\quad =\quad 36\\ { a }^{ 2 }+{ b }^{ 2 }+2\quad =\quad 36\\ { a }^{ 2 }+{ b }^{ 2 }\quad =\quad 34\\ \\ Now\quad solving\quad the\quad given\quad equation,\\ \frac { a }{ b } +\frac { b }{ a } +1981\\ \frac { a^{ 2 }+{ b }^{ 2 } }{ ab } +1981\\ \frac { 34 }{ 1 } +1981\\ 2015

CHEERS!:)

I have done same way like you have done.

Mridul KHARE - 6 years, 4 months ago

1 a + 1 b = b + a a b = 6 a b = 6 \frac{1}{a}+\frac{1}{b}=\frac{b+a}{ab}=\frac{6}{ab}=6 Dividing both sides by 6 6 we get: 1 a b = 1 s o a b = 1 \frac{1}{ab}=1\;so\;ab=1 Squaring both sides of a + b = 6 a+b=6 ,we get: ( a + b ) 2 = 6 2 (a+b)^2=6^2 a 2 + 2 a b + b 2 = 36 a^2+2ab+b^2=36 Replacing the value of a b ab in this equation we get: a 2 + 2 ( 1 ) + b 2 = 36 a^2+2(1)+b^2=36 a 2 + b 2 = 36 2 = 34 a^2+b^2=36-2=\boxed{34} Now we can solve a b + b a + 1981 \frac{a}{b}+\frac{b}{a}+1981 as follows: Rearrange a b + b a t o g e t a 2 + b 2 a b \frac{a}{b}+\frac{b}{a}\;to\;get\;\frac{a^2+b^2}{ab} Replacing the respective values in the equation we get: 34 1 + 1981 = 34 + 1981 = 2015 \frac{34}{1}+1981=34+1981=\boxed{2015}

Rudresh Tomar
Nov 13, 2014

T h e a n s w e r i s : " T H E N E X T Y E A R " The\quad answer\quad is:\\ "THE\quad NEXT\quad YEAR"

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