A homeowner wishes to insulate her attic with fiberglass insulation to conserve energy. The insulation comes in 40-cm wide rolls that are cut to fit between the rafters in the attic.if the roof is 7 m from peak to eave and the attic space is 3 m high at the peak, how long does each of the pieces of insulation need to be? Round to the nearest tenth.

the formula i need to us for this
if i am correct
7^2m-3^2m=40m
am i corect with this

That is the right formula, however, you failed to take the square root of 40.

length=sqrt(40) meters.

7^2m-3^2m=40^2m
49m-3^2m=40^2m
49m-9m=40^2m
40m=40^2m
40m=1600m