The product of two rational numbers is rational.

The product of two rational numbers is always rational

Proof:

Let a = p/q and b = r/s be two rational numbers. We will have p,q,r,s be integers where denominators q and s are nonzero. We cannot divide by zero.

Multiplying a and b gives

a*b = (p/q)*(r/s) = (p*r)/(q*s)

Due to the closure property of integer multiplication, the expressions p*r and q*s are integers. The result we get is in the form of integer/integer. Basically we have two integers being divided. Furthermore, q*s is nonzero as neither q nor s is zero.

Therefore, if a and b are rational, then a*b is also rational as well.

  about 5.6 days

step-by-step explanation:

we can fill the given information into the decay equation and solve for the value of t at which half the sample remains.

the half-life is about 5.6 days.

last option

step-by-step explanation:

given that δdef is right and isoceles,

assuming that side df is the hypotenuse means that de an ef are the other 2 sides that intersect at 90° and are of equal length.

because they are of equal length, we can say that they are congruent

because they intersect at 90°, their slopes must be opposite reciprocals.

only the last option satisfies these conditions.