Question

Marco is 8 years younger than his brother Paolo. If their product of their ages is 105, how old is Marco? plz help

Answer 1

Answer:

Marco's age is 7 years old

Step-by-step explanation:

Let

x ----> Marco's age

y ----> Paolo's age

we know that

$x=y-8$ ----> $y=x+8$ ----> equation A

$xy=105$ ----> equation B

substitute equation A in equation B

$x(x+8)=105$

$x^2+8x-105=0$

Solve the quadratic equation

The formula to solve a quadratic equation of the form

$ax^{2} +bx+c=0$

is equal to

$x=\frac{-b(+/-)\sqrt{b^{2}-4ac}} {2a}$

in this problem we have

$x^2+8x-105=0$

so

$a=1\\b=8\\c=-105$

substitute in the formula

$x=\frac{-8(+/-)\sqrt{8^{2}-4(1)(-105)}} {2(1)}$

$x=\frac{-8(+/-)\sqrt{484}} {2}$

$x=\frac{-8(+/-)22} {2}$

$x=\frac{-8(+)22} {2}=7$

$x=\frac{-8(-)22} {2}=-15$

Remember that the solution cannot be a negative number

so

The solution is x=7

therefore

Marco's age is 7 years old