Question 910595
Use the rule:
{{{ 1/a^b = a^(-b) }}}
{{{ 1/y^11 = y^(-11) }}}
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Now the expression looks like:
{{{ y^4 * y^(-11) }}}
Now use the rule:
{{{ a^b * a*c = a^( b+c ) }}}
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{{{ y^4 * y^(-11) = y^( 4 - 11 ) }}}
{{{ y^( 4 - 11 ) = y^(-7) }}}