How do you combine like terms in #(- 9u^{2} + 8u ) + ( - 5u - 4)#?

1 Answer
Tony B
Sep 13, 2016

#-9u^2+3u-4#

Explanation:

The plus in front of the right hand side bracket does not change any of the signs inside that bracket. If it had been minus then it would have changed the signs.

Consider just the right hand side brackets #->+(-5u-4)#

Treat the #color(magenta)(+)# as multiply everything inside the RHS bracket by #+1#

#(-9u^2+8u)" "color(magenta)(+)" "(-5u-4)#
#" "-9u^2+8u" "-5u-4#

#-9u^2+3u-4#

.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#color(blue)("To assist understanding using a different question")#

#color(brown)("Suppose the question had been:")#

#color(brown)((-9u^2+8u)" "-" "(-5u-4))#

Treat the #color(red)(-)# as multiply everything inside the RHS bracket by #-1#

#(-9u^2+8u)" "color(red)(-)" "(-5u-4)#
#" "-9u^2+8u" "+5u+4#

#-9u^2+13u+4#

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