數學（求積）＜＜＜急

3.

As we know , AB=AC=40

So Area of ABC = 40 x40 x0.5=800

VA^2+AB^2=VB^2

VA^2+40^2=50^2

VA=30

So , the volume of the VABC = (1/3)(30)(800)=8000//

Since VPQ and VAC are samilar

so

PQ/AC=VP/VA

12/15=VP/VP+10

12VP+120=15VP

VP=40////

b)

as same as a) part

PR=9.6//

C)ABCQPR

=VABC-VRPQ

=0.5x1/3x12x15x40 -0.5 x 1/3 x 9.6 x 12x8

=1046.4//

3.錐體體積=1/3底面積乘高
=1/3ABC * VA
=1/3*40*50/2 * 30 (VA=開方根 50^2- 40^2)
=10000 (cm^3)
8.a) VA:VA-10=15:12
3VA=150
VA=50cm
b) PR:12=40:50
PR=9.6cm
c) 1/3(15*12/2*50-12*9.6/2*40)
=732(cm^3)

sorry!我唔識做幫唔de你!