The pairs of triangles that can be proven congruent by the hl theorem is the right angled triangle.
<h3>What is mearnt be the HL theorm?</h3>
The HL theorem is also known as the Hypothenus Leg theorem, it states that "the hypotenuse and leg of one right triangle are congruent to the hypotenuse and leg of another right triangle, then the two triangles are congruent."
Learn more about the postulates of the HL theorem here:
brainly.com/question/25922842
 
        
             
        
        
        
Answer:
a) 9.72 mm
b) 4.86 mm
Explanation:
wave length of light  λ is  580 nm = 580 \times 10⁻⁹ m
Width of slit d = 0.215\times 10⁻³ m
Distance of screen D  = 1.8 m.
Width of one fringe = 
Putting the values we get fringe width
= 
=4.86 mm.
a) Width of central maxima = 2 times width of one fringe 
= 2 times 4.86 
=9.72 mm
b) width of each fringe except central fringe  is same , no matter what the order is.Only brightness changes .
So width of either of the two first order bright fringe will be same and it will be  
= 4.86 mm.
 
        
             
        
        
        
The simplest way to do this is to set up equivalent fractions, like this- 

 = 

Solve for x by using cross multiplication. 
40*2.2= 88
1*x=88
x=88
Therefore, the boy weighs 88lbs.