Xavier said the product of a monomial and a binomial will always be a trinomial. Explain the error in his reasoning.

All that is needed is a single counter-example.

One counter-example is to multiply the monomial x^3 with the binomial x^7-10x^4

We then get...

x^3*(x^7-10x^4) = x^3*x^7 + x^3*(-10x^4)

x^3*(x^7-10x^4) = x^10 - x^7

The result we get is a binomial as there are still only two terms here. We would need three terms to have a trinomial.

See below.

Step-by-step explanation:

Each term in the binomial ( there are 2 terms, by definition) is multiplied by the single term (monomial) so the answer will be  another binomial.

For example:

2x (x - 6)

= 2x^2 - 12x.

let soccer = x and golf = y

part a

1st equation: x + y = 125

2nd equation: x = y +45

part b

replace x in the 1st equation with the 2nd one:

y + 45 + y = 125

simplify:

2y + 45 = 125

subtract 45 from each side:

2y = 80

divide both sides by 2:

y = 80/2

y = 40

she plays golf for 40 minutes.

part c

no because she plays soccer for 45 minutes longer than golf 40 +45 =   85 minutes, not 80 minutes.