No.046 Find the Equation of Direct Proportion
POINT
① For direct proportion, start with y = ax.
② Substitute the known x and y values to find a, then write the equation.
② Substitute the known x and y values to find a, then write the equation.
PROBLEM
y is proportional to x, and y = 1 when x = −2.
① Express y in terms of x.
② Find y when x = 6.
③ Find x when y = −4.
Watch. Think. Try.
Try it yourself.
Make an equation and solve it. Then reveal the answer.
01
y is proportional to x, and y = 6 when x = 2. Express y in terms of x.
\(y = 3x\)
02
y is proportional to x, and y = −8 when x = 4. Find y when x = −3.
6
03
y = 4x. Find x when y = −20.
\(-5\)
04
y is proportional to x, and y = 15 when x = 5. Express y in terms of x.
\(y = 3x\)
05
y is proportional to x, and y = −6 when x = 2. Find y when x = −4.
\(12\)