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اكتب في صيغة (a-b)² أو (a+b)² الأعداد التالية : 11-6√2 ; 12+2√35 ; 5-2√6 ; 14+4√10 ; 27-10√2 ; 27+10√2 اثبت أن: √27+10√2 + √27−10√2 = 10

Mathematics

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Answer

27+102+27−102=10\sqrt{27+10\sqrt{2}} + \sqrt{27-10\sqrt{2}} = 10

14+410+14−410=210\sqrt{14+4\sqrt{10}} + \sqrt{14-4\sqrt{10}} = 2\sqrt{10}

Step-by-step solution

4 steps

Here are the proofs for the given equalities.

  1. Prove 27+102+27−102=10\sqrt{27+10\sqrt{2}} + \sqrt{27-10\sqrt{2}} = 10.

    We need to express the terms under the square roots as perfect squares.
    Notice that 27+10227+10\sqrt{2} can be written as (a+b)2=a2+2ab+b2(a+b)^2 = a^2+2ab+b^2.
    We have 2ab=1022ab = 10\sqrt{2}, so ab=52ab = 5\sqrt{2}.
    If we choose a=5a=5 and b=2b=\sqrt{2}, then a2+b2=52+(2)2=25+2=27a^2+b^2 = 5^2 + (\sqrt{2})^2 = 25+2 = 27.
    So, 27+102=(5+2)227+10\sqrt{2} = (5+\sqrt{2})^2.
    Similarly, 27−102=(5−2)227-10\sqrt{2} = (5-\sqrt{2})^2.

  2. Substitute the simplified terms into the first expression.

    27+102+27−102=(5+2)2+(5−2)2\sqrt{27+10\sqrt{2}} + \sqrt{27-10\sqrt{2}} = \sqrt{(5+\sqrt{2})^2} + \sqrt{(5-\sqrt{2})^2} =(5+2)+(5−2)= (5+\sqrt{2}) + (5-\sqrt{2}) =5+2+5−2= 5+\sqrt{2}+5-\sqrt{2} =10= 10

    Thus, 27+102+27−102=10\boxed{\sqrt{27+10\sqrt{2}} + \sqrt{27-10\sqrt{2}} = 10} is proven.

  3. Prove 14+410+14−410=210\sqrt{14+4\sqrt{10}} + \sqrt{14-4\sqrt{10}} = 2\sqrt{10}.

    We need to express the terms under the square roots as perfect squares.
    Notice that 14+41014+4\sqrt{10} can be written as (a+b)2=a2+2ab+b2(a+b)^2 = a^2+2ab+b^2.
    We have 2ab=4102ab = 4\sqrt{10}, so ab=210ab = 2\sqrt{10}.
    If we choose a=2a=2 and b=10b=\sqrt{10}, then a2+b2=22+(10)2=4+10=14a^2+b^2 = 2^2 + (\sqrt{10})^2 = 4+10 = 14.
    So, 14+410=(2+10)214+4\sqrt{10} = (2+\sqrt{10})^2.
    Similarly, 14−410=(2−10)214-4\sqrt{10} = (2-\sqrt{10})^2.

  4. Substitute the simplified terms into the second expression.

    14+410+14−410=(2+10)2+(2−10)2\sqrt{14+4\sqrt{10}} + \sqrt{14-4\sqrt{10}} = \sqrt{(2+\sqrt{10})^2} + \sqrt{(2-\sqrt{10})^2}

    Since 2−102-\sqrt{10} is negative (because 10≈3.16\sqrt{10} \approx 3.16), (2−10)2=∣2−10∣=−(2−10)=10−2\sqrt{(2-\sqrt{10})^2} = |2-\sqrt{10}| = -(2-\sqrt{10}) = \sqrt{10}-2.

    =(2+10)+(10−2)= (2+\sqrt{10}) + (\sqrt{10}-2) =2+10+10−2= 2+\sqrt{10}+\sqrt{10}-2 =210= 2\sqrt{10}

    Thus, 14+410+14−410=210\boxed{\sqrt{14+4\sqrt{10}} + \sqrt{14-4\sqrt{10}} = 2\sqrt{10}} is proven.

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