Solve: 81a² - 4 =0?
回答 (10)
2008-06-20 7:13 pm
✔ 最佳答案
it's a perfect square(9a-2)(9a+2)=0
therefore
9a-2=0
9a=2
a=2/9, a=-2/9
2008-06-21 2:13 am
Difference of two squares:
(9a - 2)(9a + 2) = 0
9a ± 2 = 0
9a = ±2
a = ±2/9
(9a - 2)(9a + 2) = 0
9a ± 2 = 0
9a = ±2
a = ±2/9
2008-06-21 2:15 am
81a² - 4 =0 Factor it first:
Take the root of 81 and 4. Place them likewise.
(9a 2)(9a 2)
In a problem such as this in which there are two squared terms separated by a minus sign, the factoring uses one '+' and one '-' to complete the factored equation.
(9a + 2)(9a - 2) Now solve for a in each factored term:
a = -2/9, 2/9
Take the root of 81 and 4. Place them likewise.
(9a 2)(9a 2)
In a problem such as this in which there are two squared terms separated by a minus sign, the factoring uses one '+' and one '-' to complete the factored equation.
(9a + 2)(9a - 2) Now solve for a in each factored term:
a = -2/9, 2/9
2008-06-22 2:10 am
a² = 4/81
a = ± 2/9
a = ± 2/9
2008-06-21 2:37 am
see 9a*9a=81a^2
2*2=4
81a² - 4 = 0
=>(9a + 2)(9a - 2) = 0
=>(9a + 2) = 0 or (9a - 2) = 0
a = -2/9 or a = 2/9
2*2=4
81a² - 4 = 0
=>(9a + 2)(9a - 2) = 0
=>(9a + 2) = 0 or (9a - 2) = 0
a = -2/9 or a = 2/9
2008-06-21 2:31 am
a^2 - b^2 = (a + b)(a - b)
81a^4 - 4 = 0
(9a^2 + 2)(9a^2 - 2) = 0
9a^2 + 2 = 0
9a^2 = -2
a^2 = -2/9
a = 屉(-2/9) (imaginary number)
9a^2 - 2 = 0
9a^2 = 2
a^2 = 2/9
a = 屉(2/9)
a = (屉2)/3
â´ a = (±â2)/3
81a^4 - 4 = 0
(9a^2 + 2)(9a^2 - 2) = 0
9a^2 + 2 = 0
9a^2 = -2
a^2 = -2/9
a = 屉(-2/9) (imaginary number)
9a^2 - 2 = 0
9a^2 = 2
a^2 = 2/9
a = 屉(2/9)
a = (屉2)/3
â´ a = (±â2)/3
2008-06-21 2:24 am
81a² - 4 = 0
81a² = 4
a² = 4/81
a = sq. rt. (4/81)
a = +/-(2/9)
81a² = 4
a² = 4/81
a = sq. rt. (4/81)
a = +/-(2/9)
2008-06-21 2:17 am
81a^2 = 4
a^2 = 4/81
a = + or - square root 4/81
a = + or - 2/9
a^2 = 4/81
a = + or - square root 4/81
a = + or - 2/9
2008-06-21 2:14 am
81a² - 4 = 0
(9a + 2)(9a - 2) = 0
(9a + 2) = 0 OR (9a - 2) = 0
a = -2/9 OR a = 2/9
(9a + 2)(9a - 2) = 0
(9a + 2) = 0 OR (9a - 2) = 0
a = -2/9 OR a = 2/9
2008-06-21 2:13 am
+- 2/9
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