Pure Flashcards
Critical damping
Discriminant of AE is 0
Underdamping
Discriminant is negative
Overdamping
Discriminant is positive
Scaler product
a.b=|a|.|b|cosx
Vector equation of a plane
(r-a).n=0
Cartesian equation of a plane
n1x+n2y+n3z+d=0
Find angle between two planes
Use scalar product on normals
Vector equation of a line in 2d
R=a+¥d
Cartesian equation of line 2d same for 3d
¥= x-a/d=y-a1/d1
Special case for Cartesian equation of a line in 3D
When d=0 write as x=a , ¥=y-a1/d1
Intersection of two lines in 2d
Solve direction simultaneously
How to prove to lines in 2d are skew
No unique solution simultaneously
Enlargement scale factor k about origin
(K 0)
O k
Stretch scale factor m parallel to x axis
(m 0)
0 1
Stretch scale factor n parallel to y axis
(1 0)
0 n
Rotation 90 degrees clockwise about origin and any rotation about origin through x degrees
(0 1)
(-1 0)
(Cosx -sinx)
(Sinx cosx)
Reflection in x and y axis
X axis (1 0) (0 -1)
Y axis (-1 0) (0 1)
Reflection y=x
(0 1)
1 0
Equation of a shear
Shear x axis fixed (1 k)
(0 1)
Y axis fixed (1 0)
(k 1)
How do you rotate 3D shapes
Check book if unsure
What is an invariant point
A point that doesn’t change when multiplied by a matrix
How to find a line of invariant points
Set up a matrix equation will lead to two equations like ax + by = 0, if unique solution then line of invariant points, if not origin only point of invariance
What is an invariant line
Any point of a line maps to another point on the line
Work out a invariant line
Suppose for y = mx + c * Multiply matrix and (x y) = (x’ y’) Use * As invariant line y’=mx’ + c Rearrange for m=0 Once solved quadratic for this Put back into x’ and y’ equations Gives invariant lines
Reflection in a plane
(-1 0 0)
(0 1 0)
(0 0 1)
Reflection in plane x=0
Inverse of a 2x2 matrix
M^-1 = 1/(ad-bc) (d -b)
(-c a)
What is it called if detm = 0
Singular
Proof for inverse of a product of matrices
x(mn) = i xmnn^-1 = in^-1 xm = n^-1 xmm^-1 = n^-1m^-1 x = n^-1m^-1
Inverse of a 3x3 matrix
1/det m (inverse)