Trigonometric area formula: area = 1/2 ab sin(c) what is the area of triangle def? round to the nearest tenth of a square unit. 10.3 square units 18.0 square units 20.0 square units 20.6 square units

1.  10.3 square units.

Step-by-step explanation:  

The general formula for area of triangle is . We can also find area of a triangle using trigonometric area formula.

, where a represents length of base and height of triangle is represented by .  

We have been given two angle measures but we can only use sine of included angle whose two side lengths are given. In our triangle the angle that measures 31 degrees in included angle of sides EF and DF.  

Now let us substitute our given values in the above formula.  

Therefore, the area of triangle DEF is 10.3 square units and 1st option is the correct choice.

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step-by-step explanation:

(0,-3) see attached graph

step-by-step explanation:

a. to solve the system, graph the two equations.

x = y+3 becomes y=x-3 has m=1/1 and b=-3. start at (0,-3) on the y-axis and plot a point. then move up 1 unit and 1 unit to the right. plot a point and connect.

y=-4x+3 has m =-4/1 and b=-3. start at (0,-3) on the y-axis and plot a point. then move down four units and to the right 1 unit. plot a point and connect.

the solution is the point (x,y) where the two lines intersect. by the graph below it is (0,-3).

b. to solve by substitution, substitute y = -4x-3 into x= y+3

x= (-4x-3) +3

x=-4x

5x=0

x=0

now substitute x = 0 back in to find y.

y= -4(0)-3

y=0-3

y=-3

solution is (0,-3)

c. use elimination by adding the equations together.

x-y=3

4x+y=-3

5x=0

x=0

then substitute into one equation to find y.

y=-4(0)-3

y=-3