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    Toughie !

    Given that the line with the equation y=x+k is a tangent to the circle x²+y²=25. Fine the two possible values ok K
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    +5 and -5.

    The circle has centre (0,0), radius 5. The line has a gradient of zero, if you just picture it in your head you can see why.
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    (Original post by Fenchurch)
    Toughie !

    Given that the line with the equation y=x+k is a tangent to the circle x²+y²=25. Fine the two possible values ok K
    x² + (x + k)² = 25

    x² + x² + 2kx + k² - 25 = 0

    2x² + 2kx + k² - 25 = 0

    Discriminant = 4k² - 8(k² - 25) = 0

    -4k² + 200 = 0

    k² = 50

    k = ±√50

    k = ±5√2

    Hope this helps,

    ~~Simba
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    The answer is ±5√2 but i dunno how to get there lol
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    (Original post by Fenchurch)
    The answer is ±5√2 but i dunno how to get there lol
    Check my post ... ±√50 = ±5√2
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    Soz Simba :P didnt see your post above, was just bout to say, n00b me √50 i obv 5√2 :P

    Simba is maths god :cool:
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    Hehe, no problem , thanks for the compliment !
 
 
 
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