几道数学题Which of the following is the modulus of 2+i?

几道数学题Which of the following is the modulus of 2+i?
1\What is the length of the line segment in xy-coordinate with end point at(1,-3)and (3,1)?
2\Express the point(2,2π/3) in terms of rectangular coordinates?
3\In △ABC.a=3,b=根号7,c=2,then the degree of angle B is
4\If 0

郭敦顒回答：1\What is the lengthof the line segment in xy-coordinate with end point at(1,-3)and (3,1)?
xy=√[（3－1）²+（1+3）²]=4√2.2\Express the point(2,2π/3) in terms of rectangular coordinates?
点(2,2π/ 3)在直角坐标系中的位置如2题图所示.3\In △ABC.a=3, b=根号7,c=2, then the degree of angle Bis ?
在△ABC中,a=3, b=√7,c=2,∠B等于多少度?按余弦定理：cosB=（a² +c²－b²）/（2ac）=（9+4－7）/（2×3×2）=6/12=1/2cosB=1/2,∴∠B=60°.4\If 0<θ<90°, then（1/cosθ-sinθ/tanθ）（cosθ）=?（1/cosθ-sinθ/tanθ）（cosθ）=cosθ/cosθ－cosθsinθ/（sinθ/ cosθ）=1－cos ²θ= sin²θ.5\Find the number ofdegrees in sin-1根号2/2?（-1是上角标）此题表达得不完整,无法解答.如果是sin－1θ=（1/2）√2,求θ,1/sinθ=（1/2）√2,sinθ=1/[（1/2）√2]=√2则无解.6\What is they-intercept of the line tangent to the circle x²+y²=1 at the point (3/5,4/5)?
过圆X²+ Y²= 1的切点P（3／5,4 / 5）的切线AB在Y轴上的截距为OB,求OB,法线OP的斜率k=（4/5）/（3/5）=4/3,切线AB的斜率k1=－1/（4/3）=－3/4,AB的切线方程,按点斜式有：y－4/5=（－3/4）（x－3/5）=（－3/4）x+9/20y=（－3/4）x+5/4,x=0时,y=5/4,切线AB在Y轴上的截距为5/4.7\The graph of theparametric equation ｛ x=1+2cosθ
                                                                    y=-2+3sinθ       is an
求参数方程{ x = 1 + 2 cosθ,y = 2 + 3 sinθ的图象,给出θ不同的数值代入x = 1 + 2 cosθ,y = 2 + 3 sinθ,求得不同的关于x、y的多组坐标,在x、y的直角坐标系中进描点即得,你自已做吧.8\A hyperbola Bellipse C parabola D circle E linesegment
题意不明.9\What is the radiusof the largest sphere that fill inside a cube with edges of length 1?
边长不1的正方体的内切最大球体的半径为R,则R=1/2.10\Which of thefollwing is not a factor of x^5+x^3+2x²-12x+8?
Ax-1 B x+2     Cx-2i Dx²+4 Ex-2
10\Which of the following is not a factor of x^5+x^3+2x²-12x+8?Ax-1 B x+2 X-2i Dx²+4X-210\下列哪一项不是X ^5+ X^3+2x²-12X+8的一个因素?AX-1 ,B X +2,×-2I,Dx²+4, X-2×-2i为复数,不是X ^5+ X^3+2x²-12X+8的一个因式.（题太多该休息一下了.）                                               Y             Y                                                                                      B （0,5/4）                     •(2,2π/ 3)                  P（3／5,4 / 5）          O                             O                    A                                X                                  X               2题图                           5题图