Given that:

**Sanjana Das** · September 26th 2009, 08:58 AM

$(1+cosA)(1+cosB)(1+cosY)=(1-cosA)(1-cosB)(1-cosY)<br />$

Show tht one of the values of each member of this equality is sinA sinB sinY.

plss explain with all the steps as i m in 10th std.....

**Grandad** · September 26th 2009, 09:23 AM

Hello Sanjana Das

Originally Posted by Sanjana Das

$(1+cosA)(1+cosB)(1+cosY)=(1-cosA)(1-cosB)(1-cosY)<br />$

Show tht one of the values of each member of this equality is sinA sinB sinY.

plss explain with all the steps as i m in 10th std.....

Multiply both sides by $(1+\cos A)(1+\cos B)(1+\cos Y)$ , noting that, on the RHS, $(1-\cos A)(1+\cos A) = (1-\cos^2A), ...$ etc:

$(1+\cos A)^2(1+\cos B)^2(1+\cos Y)^2=(1-\cos^2A)(1-\cos^2B)(1-\cos^2Y)$

Can you complete it now? (Hint: $1-\cos^2A=\sin^2A$ )

Grandad

**Sanjana Das** · September 26th 2009, 09:24 AM

Originally Posted by Grandad

Hello Sanjana DasMultiply both sides by $(1+\cos A)(1+\cos B)(1+\cos Y)$ , noting that, on the RHS, $(1-\cos A)(1+\cos A) = (1-\cos^2A), ...$ etc:

$(1+\cos A)^2(1+\cos B)^2(1+\cos Y)^2=(1-\cos^2A)(1-\cos^2B)(1-\cos^2Y)$

Can you complete it now? (Hint: $1-\cos^2A=\sin^2A$ )

Grandad

ya thxxxxxx

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