Geometry · Foundation · 5 min

Tangents to circles

From a point outside a circle, two equal tangent segments meet the circle at right angles to its radii.

WHAT HAPPENS IF…With R=1.5 and OP=2.5, what is PT?
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Loading the mathematical model…

Connect the picture to the ideaPT=OP2−R2PT=\sqrt{OP^2-R^2}

At tangency, OT is perpendicular to PT. Pythagoras in triangle OTP gives PT²=OP²−R². Reflecting across OP produces the second tangent with the same length. The construction assumes OP>R.

A detail that matters

A line that cuts through the circle is a secant, not a tangent.

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One idea leads to another.

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