SAT Math · Linear equations in two variables · medium

For every value of k, the line y = k(x-3) + 5 passes through the same fixed point, regardless of the value of k. What is the y-coordinate…

For every value of kk, the line y=k(x−3)+5y = k(x-3) + 5 passes through the same fixed point, regardless of the value of kk. What is the yy-coordinate of that point?

Answer and explanation

Answer: 5

The line is written as y=k(x−3)+5y = k(x - 3) + 5. If x=3x = 3, the term k(x−3)k(x-3) becomes k⋅0=0k \cdot 0 = 0 no matter what kk is, leaving y=5y = 5. So every line in the family passes through the point (3,5)(3, 5), and the yy-coordinate is 5. This is point-slope form, y−y1=m(x−x1)y - y_1 = m(x - x_1), with m=km = k, x1=3x_1 = 3 and y1=5y_1 = 5, so the fixed point can be read straight from the equation. A common wrong answer is −3-3, which comes from taking the number inside the parentheses, and another is 2, from computing 5−35 - 3.

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