Help me what is the Answer?

How to choose the sign of the radical in the denominator of the formula for the distance from a point to a line.

What is the number 321,000,000 in scientific notation? also what is the number? ?

Johnny rode his bike to a friends house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was unable to play. what was his displacement for the total bike ride trip? what could you use as a reference point ? show the steps to solve this problem.