It took Brian 6 hours to drive to the sales conference. He took the same route on the way back home, but
thus time the trip took 7 hours. If Brian drove 9 mph faster on his way to the conference, how fast did he
drive on the way back home?

 54 mph

Step-by-step explanation:

d-the distance

s+9  -  the speed to the conference

d=6*(s+9)

s- is the speed on the way back home

d=7*s

so    6*(s+9)=7*s

       6s+54=7s

     -6s          -6s

       54= 7s-6s

       s=54  mph

  or  

step-by-step explanation:

if the four friends split the cost, p, of the pizza evenly, then each friend pays one-fourth of the cost of the pizza.

the expression is   or  

proofs involving isosceles triangles often require special consideration because an isosceles triangle has several distinct properties that do not apply to normal triangles.(more about triangle types) therefore, when you are trying to prove that two triangles are congruent, and one or both triangles, are isosceles you have a few theorems that you can use to make your life easier.

step-by-step explanation:

an isosceles triangle has two congruent sides and two congruent angles. the congruent angles are called the base angles and the other angle is known as the vertex angle. ∠bac and ∠bca are the base angles of the triangle picture on the left. the vertex angle is ∠abc