Built-up area

John build up area 5 x 7 = 35 m2 with building with a wall thickness 30 cm. How many centimeters would have to subtract from thickness of the walls that built-up area fell by 9%?

Correct answer:

x =  13.4 cm

Step-by-step explanation:

a=5\m b=7\m (a2x)(b2x)=(19/100)ab 4x2+x(2a2b)+ab9/100=0  4x224x+3.15=0  a=4;b=24;c=3.15 D=b24ac=242443.15=525.6 D>0  x1,2=2ab±D=824±525.6 x1,2=3±2.8657459761814 x1=5.8657459761814 x2=0.13425402381858   Factored form of the equation:  4(x5.8657459761814)(x0.13425402381858)=0  0<x<30 cm x=13.4 cm

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