(3) There are 78 lilies, roses and tulips in the florist. Among them, lilies are more than twice as many as roses, and roses are three times as many as tulips, and less than two. What's the difference No hurry!

Suppose there are x tulips
x+（3x-2）+2（3x-2）+4=78
4x-2+6x-4+4=78
10x-2=78
10x=80
x=8
So:
8 tulips
Rose = 3 × 8-2 = 22
Lily = 2 × 22 + 4 = 48
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The school has a flower bed against the wall. The width of the flower bed is 30 meters and the length is 60 meters. (1) if a fence is built around the flower bed, how long is the fence

60+30*2=120

If the formula √ 2x-1 + &# 179; √ 3-x is meaningful, then the value range of X is?

If it is meaningful, 2x-1 under the root sign is ≥ 0
So x ≥ 12

It is known that (A-3) (2a + 5) x + (A-3) y + 6 = 0 is a linear equation with one variable,

Since it is a linear equation of one variable, only x or Y has coefficients in front of it. That is to say, one of the coefficients before X or y must be 0. Suppose that the coefficient before y is 0, then A-3 = 0, and a = 3. If a = 3, then the coefficient before x is also 0, which is not desirable. Then only the coefficient before x is 0, and a is not equal to 3. So 2A + 5 = 0, and a = - 5 / 2

X-8 x-16 = 0
How to forget

x²-8x-16=0
x²-8x+16=32
(x-4)²=32
x-4=±4√2
x=4±4√2

What is the result of (3a & # 178; - 2A + 1) - (2a & # 178; + 3a-5)?

A ^ 2-5A + 6 or (X-2) (x-3)

Can x + [x + 6] + [3x-8] merge similar terms

Original formula = x + X + 6 + 3x-8
=5x-2

Geometric meaning and application examples of positive definite matrix
I learned some of its properties, but I didn't really understand them,
So we ask for the geometric meaning of positive definite matrix, and give several examples of specific applications
For example, the geometric meaning of the eigenvector is the direction invariant vector after the linear transformation, and its applications include: solving the differential equation and finding the square a ^ n of the matrix
PS: please don't just paste definitions. If you answer well, add points
Can we simply explain that "positive definite matrix does not change the shape of a graph when it makes a linear transformation of a graph in three-dimensional space"? Xxp90, your geometric meaning is very good, then what is the main use of positive definite matrix? What's the point of mapping to the same side?

The hyperplane perpendicular to any vector x divides the space into two parts. One part and X are on the same side, that is, the side satisfying the positive inner product of X, and the other part is on the opposite side, and the inner product is negative

A (n + 1) = sin (an)

Can use monotone bounded sequence must have limit proof, as shown in the figure, and find out the limit is 0

Without changing the value of the fraction, the coefficients of the fraction 1 / 3x + 1 / 9y / 1 / 5x - 1 / 10Y are changed to integers?

（18x－9y）/(30x－10y)

(3) There are 78 lilies, roses and tulips in the florist. Among them, lilies are more than twice as many as roses, and roses are three times as many as tulips, and less than two. What's the difference No hurry!