1.

If `A (x_(1), y_(1)), B (x_(2), y_(2)) and C (x_(3), y_(3))` are vertices of an equilateral triangle whose each side is equal to a, then prove that `|(x_(1),y_(1),2),(x_(2),y_(2),2),(x_(3),y_(3),2)|` is equal toA. `2a^(2)`B. `2a^(4)`C. `3a^(2)`D. `3a^(4)`

Answer» Correct Answer - D
Let `Delta` be the area of triangle ABC. Then, `Delta = (1)/(2) |(x_(1),y_(1),1),(x_(2),y_(2),1),(x_(3),y_(3),1)| rArr 2 Delta = |(x_(1),y_(1),1),(x_(2),y_(2),1),(x_(3),y_(3),1)|`
`rArr 4 Delta = |(x_(1),y_(1),1),(x_(2),y_(2),1),(x_(3),y_(3),1)| = |(x_(1),y_(1),2),(x_(2),y_(2),2),(x_(3),y_(3),2)|`
`rArr 16Delta^(2) = |(x_(1),y_(1),2),(x_(2),y_(2),2),(x_(3),y_(3),2)|`..(i)
But, the area of an equilateral triangle with each side equal to a is `(sqrt3)/(4) a^(2)`
`:. Delta = (sqrt3)/(4) a^(2) rArr 16 Delta^(2) = 3a^(4)`..(ii)
From (i) and (ii), we obtain
`|(x_(1),y_(1),2),(x_(2),y_(2),2),(x_(3),y_(3),2)|^(2) = 3a^(4)`


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