#color(brown)("When you multiply and the signs are the same the answer is")# #color(brown)("positive. If they are not the same the answer is negative.")#
In this case they are not the same so the answer is negative.
It is mathematically wrong to say 'the answer is a minus.'
Minus is an action. Negative is a state (condition).
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#color(brown)("To avoid the decimal in the early stages of the calculation do this:")#
#12.6 = 1260xx1/100#
#0.81 = 81xx1/100#
So we have:
#1260xx81xx1/100xx1/100" "->" "1260xx81xx1/10000#
We leave the #xx1/10000# until the end
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Split 81 into #80+1#
#color(blue)("The actual calculation")#
#" "80xx1260 rarr 100800#
#" "1xx1260 ->ul(color(white)(..) 1260) larr" add"#
#" "color(white)(.)102060#
#102060xx1/10000 = 10.206larr" now we adjust the value"#
#color(blue)("But the answer is negative "-10.206#
