Question 339735
{{{7/x+7/y=9/(x+y)}}}
{{{7y+7x=9xy/(x+y)}}}
{{{7(x+y)=9xy/(x+y)}}}
{{{xy/(x+y)^2=7/9}}}
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{{{(1/(x+h)^4-1/x^4)/h =((x^4(x+h)^4)/(x^4(x+h)^4))*((1/(x+h)^4-1/x^4)/h )}}}
{{{(1/(x+h)^4-1/x^4)/h =(x^4-(x+h)^4)/(hx^4(x+h)^4)) }}}
{{{(1/(x+h)^4-1/x^4)/h =(x^4-(x^4+4hx^3+6h^2x^2+4h^3x+h^4))/(hx^4(x+h)^4)) }}}

{{{(1/(x+h)^4-1/x^4)/h =(-4hx^3-6h^2x^2-4h^3x-h^4)/(hx^4(x+h)^4)) }}}
{{{(1/(x+h)^4-1/x^4)/h =(-4x^3-6hx^2-4h^2x-h^3)/(x^4(x+h)^4)) }}}