The plane α. β. γ intersects each other, and the intersection line is ABC. A ‖ B

The plane α. β. γ intersects each other, and the intersection line is ABC. A ‖ B

Because a is parallel to B, a is parallel to α, and a C belongs to β. A is parallel to α, and C is the intersection of α and β. So a is parallel to C

If plane α intersects with planes β and γ, the three planes may have ()
A. One or two intersecting lines B. two or three intersecting lines C. only two intersecting lines D. one or two or three intersecting lines

① If plane β∩ plane γ and plane α intersect with planes β and γ, then they have two intersecting lines, and these two intersecting lines are parallel to each other; if plane β∩ plane γ = A and plane α is a plane passing through line a, then there is only one intersecting line among the three planes, namely line a; if plane β∩ plane γ = a, plane α and plane β

It is known that three planes intersect each other and there are three intersecting lines. It is proved that the three intersecting lines are parallel to each other or intersect at a point

Plane S1 and S2 intersect line L1. If S3 passes through L1, then s1s2s3 intersects on the same line, which is inconsistent with the title, so L1 is not on S3
So 1) if L1 intersects S3, intersection a, then a is on L1, then a is on S1, so a is on the intersection line of S3 and S1. Similarly, a is on the intersection line of S2 and S3, so three lines are called point a
2) If L1 is parallel to S3, then the intersection line L3 of S1 and S3 is on S3, and L1 is parallel to L3 in S1, so is L1 and L2

The calculation of the determinants of sub upper and lower triangles
Find the value of determinant | D |

By the definition of determinant, both determinants are equal to
(-1)^t(n(n-1)...21) a1na2,n-1 ...an1
= (-1)^[n(n-1)/2] a1na2,n-1 ...an1

109 degrees 23 minutes 18 seconds divided by 3 =?
73 ° =? 86 ° 32 ′ 18 ″ about? 23 ° 45 min + 24 ° 15 min =? 90 ° 35 ° 45 min 1 s =?

52.73°=52°43′48〃
86°32′18〃=86.5383333…… ≈86.54°
23°45′+24°15′=48°
90°-35°45′1〃=54°14′59〃

If a function f (x) has f (x0) = x0 for a certain number x0 in its domain, then x0 is said to be a fixed point of F (x)
If the function f (x) = ax ^ 2 + (B + 1) x + B-1 (a ≠ 0) is used to find ① a = 1, B = - 2, the fixed point of function f (x) can be found. ② if there are two fixed points of function f (x) for any real number B, the value range of a can be found

① When a = 1, B = - 2, f (x) = x & sup2; - x-3, let X & sup2; - x-3 = x, then the solution is x = 3, or x = - 1, the fixed point is (3,3), (- 1, - 1) ② let ax ^ 2 + (B + 1) x + B-1 = x, and the result is that ax & sup2; + BX + B-1 = 0, ∵ the equation has two unequal real roots ∵ Δ = B & sup2; - 4a (B-1) = B & sup2; - 4A

Simple calculation: 49 / 5 × 7 / 8 △ 7

49/5×7/8÷7
=49/5×(7/8÷7)
=49/5×1/8
=49/40

If x + 2Y + 3x = 103x + 3Y + 5Z = 15, then the value of X-Y-Z is

Right Title:
x+2y+3z=10 （1）
3x+3y+5z=15（2）
(1) The formula is multiplied by 2
2x+4y+6z=20 (3)
(2) (3)
x-y-z=-5.

Simple operation 980 divided by 35

980/35=980/7/5=140/5=28.

When a straight line passes through point P (3,2), the inclination angle is twice of the inclination angle of the straight line X - 4Y + 3 = 0?
Wrong question. Why is the slope of the straight line 8 / 15?

X - 4Y + 3 = 0, the slope TaNx = 1 / 4 twice is tan2x = 2tanx / (1 - (TaNx) ^ 2) = 8 / 15