The altitude of a triangle is 5m less than its base the area of the triangle is 42 find the base

A = (1/2) bh

h=height=altitude

h=b-5

area=42

42 = (1/2) bh

times 2

84=bh

sub b-5 for h

84=b (b-5)

84=b²-5b

minus 84

0=b²-5b-84

factor

what 2 numbres multiply to get - 84 and add to get - 5

-12 and 7

0 = (b-12) (b+7)

set to zero

b-12=0

b=12

b+7=0

b=-7, false, can't have negative measures

so

b=12

the base is 12m