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ICSE Class 7 Answered

if 2l-3m=-1 and lm=20 then ,the value of 4l2 +9m2

Asked by h3k.behera | 16 Aug, 2015, 09:32: PM
answered-by-expert Expert Answer
G i v e n space t h a t space 2 l minus 3 m equals negative 1 space a n d space l m equals 20 N o w space c o n s i d e r space s q u a r i n g space t h e space g i v e n space e q u a t i o n comma space w e space h a v e comma open parentheses 2 l minus 3 m close parentheses squared equals open parentheses negative 1 close parentheses squared rightwards double arrow 4 l squared plus 9 m squared minus 2 cross times 2 l cross times 3 m equals 1 space space space space space space space space space open square brackets because open parentheses a minus b close parentheses squared equals a squared plus b squared minus 2 a b close square brackets rightwards double arrow 4 l squared plus 9 m squared minus 12 l m equals 1 rightwards double arrow 4 l squared plus 9 m squared minus 12 cross times 20 equals 1 space space space space space space space space space space space space space open square brackets because space g i v e n space t h a t space l m equals 20 close square brackets rightwards double arrow 4 l squared plus 9 m squared minus 240 equals 1 rightwards double arrow 4 l squared plus 9 m squared equals 240 plus 1 space space rightwards double arrow 4 l squared plus 9 m squared equals 241
Answered by Vimala Ramamurthy | 17 Aug, 2015, 08:49: AM

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