Algebra · real student question

The equation y = p times the square root of x plus q divided by the square root of x is non-linear. Change it to a linear form.

Question

The equation

y=px+qxy=p\sqrt{x}+\frac{q}{\sqrt{x}}

is non-linear. Change it to a linear form.

Step-by-step solution

  1. Fix what "linear form" is asking for. The goal is an equation Y=mX+cY=mX+c in which YY and XX are expressions built from xx and yy, and the unknown constants pp and qq appear only as the gradient and the intercept. Then plotting YY against XX from experimental data gives pp and qq from the line.

  2. Identify what blocks that form. As written, the right-hand side contains both x\sqrt{x} and x1/2x^{-1/2}. No choice of XX makes a sum of two different powers linear, so the equation has to be reshaped before any variable is renamed.

  3. Multiply both sides by x\sqrt{x}. Since x>0x>0 is required for x\sqrt{x} to be defined and nonzero, this is a legal operation:

    yx=pxx+qxx=px+qy\sqrt{x}=p\sqrt{x}\cdot\sqrt{x}+\frac{q}{\sqrt{x}}\cdot\sqrt{x}=px+q

    The two awkward half-powers collapse: one becomes xx, the other becomes a constant.

  4. Name the new variables and read off the constants. Setting

    Y=yx,X=xY=y\sqrt{x},\qquad X=x

    the relation is Y=pX+qY=pX+q: a straight line whose gradient is pp and whose vertical intercept is qq.

  5. Check with concrete numbers. Take p=2p=2, q=3q=3 and x=4x=4. The original equation gives y=2(2)+32=5.5y=2(2)+\tfrac{3}{2}=5.5, so Y=yx=5.5×2=11Y=y\sqrt{x}=5.5\times 2=11. The linear form predicts pX+q=2(4)+3=11pX+q=2(4)+3=11 — identical, confirming the transformation preserves the relation rather than just looking tidier.

Answer

yx=px+q,i.e. Y=pX+q with Y=yx, X=xy\sqrt{x}=px+q,\qquad\text{i.e. }Y=pX+q\ \text{with }Y=y\sqrt{x},\ X=x

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