ABC is an isosceles triangle with AC = BC. If AB² = 2AC², Prove that ABC is a right triangle.​

ABC is an isosceles triangle with AC = BC. If AB² = 2AC², Prove that ABC is a right triangle.​

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2 thoughts on “ABC is an isosceles triangle with AC = BC. If AB² = 2AC², Prove that ABC is a right triangle.​”

  1. The converse of the Pythagorean theorem.

    Triangle must satisfy [tex]\sf{\overline{AB}^2=\overline{BC}^2+\overline{CA}^2}[/tex] to become a right triangle.

    One of the given condition is [tex]\sf{\overline{BC}=\overline{CA}}[/tex]

    We get [tex]\sf{\overline{BC}^2=\overline{CA}^2}[/tex]

    Another given condition is [tex]\sf{\overline{AB}^2=2\overline{CA}^2}[/tex]

    [tex]\sf{\implies \sf{\overline{AB}^2=\overline{CA}^2+\overline{CA}^2}}[/tex]

    [tex]\sf{\implies \overline{AB}^2=\overline{BC}^2+\overline{CA}^2}[/tex] (Right-angled at [tex]\sf{\angle{C}}[/tex])

    So we have a right triangle according to the converse of the Pythagorean theorem.

    Hence proven.

    Interesting facts

    [tex]\sf{\overline{AB}}[/tex] is √2 times the other sides.

    [tex]\sf{\implies\overline{AB}=\sqrt{2} \;\overline{BC}}[/tex]

    [tex]\sf{\implies\overline{AB}=\sqrt{2} \;\overline{CA}}[/tex]

    The triangle area is [tex]\dfrac{1}{4}[/tex] times the square of the hypotenuse.

    Pythagorean theorem was not proven by himself. It was Euclid who proven it for the first time.

    Fermat’s last theorem is similar to [tex]\sf{a^2+b^2=c^2}[/tex], but any integer satisfy over the power of 2. One of the interesting facts is Fermat didn’t prove it. 358 years since Andrew Wiles came up with the perfect proof.

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  2. Answer:

    Given, △ABC is an isosceles triangle,

    ∴ AC=BC(1)

    Also, given that,

    (AB)

    2

    =2(AC)

    2

    ∴ (AB)

    2

    =(AC)

    2

    +(AC)

    2

    (2)

    ∴ From (1) and (2)

    (AB)

    2

    =(AC)

    2

    +(BC)

    2

    Hence, By converse of Pythagoras theorem,

    △ABC is an isosceles right-angled triangle. henceproved

    hope this helped u

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